I know I've played parts written in
H, but I can't find any from Google search.
H is the German equivalent of
B. Source: http://web.library.yale.edu/cataloging/music/names-keys-french-german-italian-and-spanish
In German music, Trumpet in B actually means Bb and H means B (natural). It's quite uncommon, but I have also seen Trumpet in B (not Bb) in some French classical music as well, in one case I think it was a flute concerto, but it's been years since I played it and I do not recall the composer.
Brahms 1st Symphony is one, calls for C, E and B. Brahms 2nd as well. D and B
It's fairly rare, but you either play it on a C trumpet (down a half step on everything) or a Bb (up a half-step on everything). You get used to it after a while.
Most classical rep that's public domain now (almost all from the period where B was being used) is available on IMSLP (internet repository). If you dig around, especially under German composers, you should be able to find more examples.