Now that I have your attention. Does anyone have any info about the Wilsford flute that was found near Stonehenge or the flute that was found in the Avebury stone circle? Just to make a note…these flutes pre-date the Celts in England - so, no they are not “Druid” flutes. Not so say Druids today could not play one. 
1 flute made from the long bone of a crane (previously identified as a swan) with two holes in its side, found with a primary cremation in Bowl Barrow Wilsford G23, excavated by William Cunnington
Source:
http://history.wiltshire.gov.uk/museums/index.asp
search for Bowl Barrow Wilsford G23
Everyone knows that all the Druids were pipers.
When I read the thread title my shoulders sagged and I actually muttered aloud, “You’re kidding.” Bad Dragon. Bad, naughty Dragon. 
That was exactly my thoughts too. I’m so glad the actual post didn’t bear out my fears.
Sorry, my parser cannot deal with this statement. Perhaps some punctuation could help.
Not to say Druids today could not play one.
Thank you, Hans. 
I think all druids should play flute, or whistle.
Our woods need it.
And I’ll offer purpose-built wand-whistles, made in silver, extra long with a crystal fitted into the end. And hemp tassels. 
I trust that the underlying irony of this will not have escaped you.
It may well have!
I mean that if all those druids, robed or cloaked, would practice flute or whistle playing, they will start having some jolly times, in the woods, and out of them. That can only be good, no? Might transform the ritual aspects of druidic life into really magic moments. - Yes, no irony there.
What the woods think of that I can’t answer, except that I love playing in the wood, and no tree has yet reproached me for it. But I am not a druid.
My point being there are no stands of Delrin growth to be exploited for our magickal musickal frolicks. Or, something like that.
LOL, especially the “old growth Delrin” But the mighty Sequoya Delrin (the prehistoric predecessor) has been extinct for millenia. 
Nano is still looking for the spaghetti trees.
And I daresay they won’t thank me for eating them, either.
I regularly play Pennywhistle and Overtone Flute in the Woods. I am arguably a Druid. I am not a member of OBOD or other Druid organization, but I have participated at Druid Rites and am well-versed in Ogham. My playing may not be technically excellent, but it comes from the heart.
So far from reproach, I would say the woods seem to enjoy it.
After some digging, here’s the answer to the original question.
Split view showing interior hole diameter, length, etc.
An original from the Gallic Celtic city of Alesia
A modern reproduction.
Whaaaat? Me? Naughty? Ney! The Druids were great flute players! 
Yes yes I ment “to”
Which band? On what planet?