There is definately a piano trio by Ravel, it's quite often played. He only wrote one that's why we were refering to it as "the" Ravel trio. As for the op.1s, Beethoven published three piano trios under op.1. This is not uncommon with chamber works and sonatas, composers often publish a set of works under one opus number, some of his sonatas do the same. As for specific trios you could try op.1no.1, op.11 in Bflat (lovely piece), op.70no.2 or op.97. There are many others, but these are the ones that I really know.