So I'm a member of Seeing Stars which is pretty much the biggest and best petz horse community there is around. :3
There are many different files around, but the main ones on Seeing Stars are the Manda V1 & V2, the Havoc Horse (by Dane), and the rafa V1 & V2. The Manda V1 is available to all members of Seeing Stars (although the current download isn't working so you can PM one of the staff members on SS to acquire the file). The Manda V2 is limited to file-holders, although from time to time we do adoptions or custom hexing services, as well as surprise gifts. The havoc horse is only available from dane, and the rafa V1 is available on her site (which you can find on SS XD) and the rafa V2 is only available to certain people who do adoptions/customs/gifts.