Hello NorthernEuph,
Although I am not in the market for a euphonium, I thought that if you were in Ontario, you or your friend might consider showing his instrument at the upcoming Canadian Band Association (Ontario) Brass Band Weekend in Kincardine, ON, from April 26-28 or at the Concert Band weekend in Barrie on Father's Day weekend. The following is a link to the Kincardine event. Good luck!
https://www.kincardinebrass.ca/schedule-and-events/
Euph Loosh
Imperial by Boosey & Hawkes 4-valve Euphonium (mid-1950's)
MPs: Kosikup 1 1/2, Bowman BB2 Euro shank, Denis Wick 4AM; Marcus Bonna case