The UK has 2 native Elder species Sambucus nigra Common Elder
http://www.purplesage.org.uk/profiles/elder.htm
and Sambucus ebulus Dwarf Elder (Danewort).
http://www.highwaygold.co.uk/science/biology/flora_fauna/plantae/magnoliophyta/magnoliopsida/caprifoliaceae/sambucus/sambucus_ebulus/DSCN1739s.html
The Czech Whistles are made from Sambucus nigra which is common all over northern Europe.
John S
Here’s what is near me :
Box Elder - tree - hay-fever suffers may not be happy to find it 
http://www.naturesongs.com/vvplants/boxelder.html
http://www.unicapinvitrosight.com/templates/Allergens.asp?id=2281
http://dnr.wi.gov/org/land/forestry/treeid/TreePgs/acernegundo.htm - “Wood - Creamy white, soft, light and close-grained; decays rapidly in contact with heat and moisture; used occasionally for fuel; has no general commercial value.” - doesn’t sound like it would be good for whistles 
Elderberry - shrub/bush - wime makers may be thrilled to find it 
http://aes.missouri.edu/swcenter/fieldday/elder.stm
http://www.missouriwildflowerguide.com/Flowers/ElderberryNoteCard.html (the photo here is upside down)
The elderberries, Sambucus spp., are both the source of the pith filled branches and the edible berries. It can grow to be a small tree that could just as easily be thought of as a large shrub. I know we have at least the species Sambucus glauca here in north Idaho.
I came across an English translation of a book on how to make western European traditional musical instruments at the U of I library when I was researching how to make whistles. According to that book, people that made their own whistles out of elder were seen as lazy, just playing their lives away under the shade of the elderberry trees. The book did speak highly of the wood and the ease of pushing the pith out of the stems.
According to the book Wild Berries of the Pacific Northwest by J. E. (Ted) Underhill (a good Hobbit last name, if I’ve ever seen one!) the quality of the European elders’ wines were so high, that some countries outlawed them so they wouldn’t be fraudulently sold as grape wine. England could make good wine, despite it not having fine wine grapes, so I’ve often wondered if the taunt “your father smells of elderberries” was in reference to the English wine that a Frenchman might look down upon as being fit only to give to English drunks (the Pythons could be erudite, but I might be reading way too much into that). Personally, I’m tempted to see if any of the native elders make a good enough wine to compete head to head with the fine grape wines!
Rod
Elderberries make a good rustic red wine-o.k. it can’t compare to Pomerol,but you can make it for the cost of a few pounds of sugar,if you have the right equipment.
Elton John had a song called ‘Elderberry wine’.Maybe he’s been at it,considering his recent behaviour (maybe it’s what we in the U.K. Northeast call a’ fighting drink’! 
).
ElderFLOWERS also make a very perfumed refreshing summer drink,or a very nice white wine.
Usually,my mother makes jams from soft fruits donated from my garden-Strawberries,Raspberries,Blackcurrants,Redcurrants and Gooseberries,but last year I also picked some wild Blackberries and Elderberries.
Combined,the wild fruits made a delicious preserve with a great depth and intensity of flavour.
MMmmm! 
I was recently in the Czech Republic and used a local friend to contact Vitek Kasparik, maker of Elderflower whistles. We arranged to meet him at his home…three cell phone calls later (to find this out-of-the-way trail head) and a 15 minute hike up a small mountain, and we were at his home!
We were invited into his 1-room place which he built himself. His work shop is in a separate barn-like building. As far as I can tell, he makes his living building wind instruments, and has given up shepherding.
After a glass of water and some small talk (via my Czech translator) Vit broke out the instruments…whistles, recorders, clarinets, things with drones, a stick that sounded like a clarinet, some with bark on, others with bark off…all laid out on the kitchen table. Oh, and the rabbit skin bag pipe was also there!
He is one fine instrument maker. I ended up buying a C whistle with scalloped holes, and is sounds terrific - mostly pure with a bit of chiff. Dead on tuning (cnat oxxooo). Medium volume, not quiet but not really loud or shrill. Also bought a high D in shepherd style (no beak, windway on the bottom for wind resistance). It also has knots near the bottom hole…lots of character.
Both of these whistles are bark-less; apparently he does not sell many Irish style whistles (mostly recorders and other Moravian-style folk instruments) so an Irish style whistle with bark on is a special order…if you can reach him (I am working through my Czech friend to secure a bark on in C).
I offered to serve as his USA importer, but alas he declined…he has all the work he can handle, selling his instruments by word of mouth, and at the open air museum in a nearby town.
I have a number of fine wooden whistles - Thin Weasel, Greenwood and Busman. While all of them are more refined in appearance, the sound and charm o Vitek’s rustic whistles make them on par with the very best in the industry.
If you can get your hands on one of these things, you will not regret it.
I’ve got to agree with you. I have one (no bark) and I REALLY love it. Thanks so much for your little report: did you by any chance take any pictures? I’d love to meet that guy.
Oh great…
Now I’m going to eye that elder tree on my way to and from work even more longingly than usually.
You know, elderflower sherbet and elderberry jam are delicious.
Now, suffering from a bout of WhOA everytime I see one, I’m sure, I’m going to frighten the neighbors…
I do have some pictures but cannot seem to get them posted. Any help would be appreciated.
Guide to Posting Images: https://forums.chiffandfipple.com/t/guide-to-posting-images/22873/1
Here are some pictures from my visit to Vitek: his home, the view from his home, some of his instruments on the kitchen table, Vitek (right).
http://yfrog.com/0bczechrepublic2009093jx
Paul, where did you get your Elderflower whistle?
Wow Scott! Thanks for those pictures.
Some of those whistles have a curve to them: how the heck does he bore those???
I noticed one with double holes to make playing Fnat and Bb easier (or whatever the corresponding notes on that particular whistle are).
I had imagined Vitek to be a little old man, which he obviously is not. Great stuff.
I got my whistle from Colin Goldie as part of a whistlemaker’s trade: I traded one of mine for the Elder Flower and an anodized Overton A.
Yeah, that curve is very cool. One of the whistles I bought is in D, shepherd style with the windway on the bottom. It is very curved, and has knot bumps (symmetrically placed near the D hole). But it is pitched perfectly and totally in tune up and down the scale.
From what I could gather, he bores these by hand without mechanized assistance. The pith of Elderberry is very soft and is easily be removed…but the bore is a greater diameter than the pith, and it is perfectly smooth. Also, the windway is absolutely perfect - I have never seen them so perfectly carved and symmetrical. Not sure how he pulls all this off, but obviously he is a master of his craft.
Great whistles indeed - I’ve got one from Vítek in E, and it sings like…umm…a singer. I don’t know how it is with this model, mine has a bit too small windway, so it takes too little breath (does sound like good thing, but at this extent, not really).
Still, wonderfully clear tone, like a spring in the mountains.