Unfortunately I don't know of any repository like that. There have been a few monsters posted on the forums, and there may be a few in the Downloads section.
I have converted dozens of monsters with full stat blocks. Stuff like allip, morhg, ulgurstata, spawn of Kyuss, wind warrior, mad slasher, etc. Recently I changed tactics because the full stat blocks take too much time. Most of the time now I take the closest monster I can find out of the MM and change one or two iconic things about it that make it unique. This goes much faster and still gives me the results I want. Ari's Monster Sorter goes a long way toward quickly finding a monster that is close to what I want.
