I have found the Fraxy Compendium!
The ultimate repository of Fraxy Bosses, as well as a wiki on Fraxy itself. There's hundreds here, ranging in their quality, but a few of them are absolutely incredible.
In particular, check out the bosses by these authors: DrunkGoomba, A70M1C, and FraxyFactory.
Note: ignore that announcement on the main page about them moving to a new location. They've barely moved anything to that new area, so most of the bosses are still in the Compendium I linked to.
Anyone who missed the old thread and is interested in what exactly Fraxy is, see here.