I tried looking on YouTube for anything, but I didn't really find something useful.
I did happen to find this video with an album cover from 1994, but it looks like his instrument already has a Besson-branded trigger installed, which would make it a Prestige?
https://www.youtube.com/watch?v=Q7aVqPQiDuc
So the best way to find some kind of material is to look for anything pre-Prestige era but after 1990 since that's when he wanted to have a trigger on his euphonium.
Euphoniums
2008 Willson 2960TA Celebration
1979 Boosey & Hawkes Sovereign (Round Stamp)
Mouthpiece: Denis Wick SM4
Baritone
1975 Besson New Standard
Mouthpiece: Courtois 10