I do not have a Callet trumpet but have one of his mouthpieces that he hand lathed for my Olds Recording in his studio when I lived in New York City. An amazingly wonderful individual.
My reply is more however based on you noting the more recent maker of his trumpet, Kanstul is now defunct. I have a Kanstul that recently had an issue that I was unaware a valve cap had fallen off. I tried on line to find a replacement and had a heck of a time (I have had no problems for instance finding parts for my 1946 vintage Martin Committee).
So out of desperation, I contacted Jason Harrelson to see if he has machined caps for the Kanstul, and he did. So I got a complete set of valve caps from him and they fit and work perfectly.
So if you doe need any replacement parts for your Callet, do contact Harrelson Trumpets and they would most likely accommodate your needs.