Hello!
I come from a GHB background and piping retreats are fairly common throughout the USA, I’ve been looking for something similar for whistling and haven’t been able to find any. Basically I’m looking for a 2-5 days of focused practice in a group or individual setting. Basically something to force me to get good 
. Any suggestions?
Where are you located?
Best wishes.
Steve
Swananoa Gathering has a whistle track with Cillian Vallely and Shannon Heaton. https://www.swangathering.com/catalog/cl/classes/
Acadia Trad School has a whistle track with Hanz Araki and Shannon Heaton https://acadiatradschool.org/festival/classes/
Portal Music Week has whistle with Kevin Crawford https://portalmusicweek.com/
O’Flaherty Irish Music Retreat has Kevin Crawford and Grey Larson https://oflahertyretreat.org/instructor_role/core-classes/
That’s a start…
Best wishes.
Steve
Have you looked at the top of this whistle forum at the Whistle Instruction thread?
https://forums.chiffandfipple.com/t/whistle-instruction/100082/1
The Catskills Irish Arts Week (depending upon your location).
https://www.catskillsirishartsweek.com/summer-catskills-irish-arts-week/instructors/
I’m in Utah, anywhere in the USA / Canada is fine though.
Seattle area:
http://www.ceolcascadia.org/
Texas:
https://oflahertyretreat.org/
If you’re on Facebook:
https://www.facebook.com/Annual-Utah-Irish-Festival-136226943121912/
There must be local traditional sessions where you could meet players and get further local information. Enjoy your whistling.
Interesting, I’ve been playing Highland pipes for over 40 years and I can’t recall hearing of such a thing as a piping “retreat”.
In the Highland piping world there are large gatherings based around competition, the biggest one here in the USA being Winter Storm.
Then there are piping summer schools, run by The College Of Piping/National Piping Centre, Balmoral School of Piping, and other organisations.
https://balmoralschoolofpiping.org/balmoral-school/balmorals-summer-bagpiping/
What the Highland piping world doesn’t seem to have is something equivalent to the uilleann pipe Tionol, an informal gathering taking place over a weekend including socialising, workshops, concerts, and reedmakers trying to get everyone’s pipes going.
(BTW in Highland piping a “gathering” and a “retreat” are tune-types.)