I once rang up Farmkey about a LOU mare I had found a home as a companion and she was then sold! They said they werent allowed to give me any details but that she was still registered to me and they would put a note on the computer so that if a new owner wanted to trace her history I would allow contact.
i also got in touch with Farmkey about a mare i had. They also said that they would contact the new owner and say that i was interested in hearing how she was.
Also tried it with where the mare was registered (SHBGB) they said that they would write/call the owner for me if i wanted.
Is your horse registered anonmouse? have you tried contacting them to see if they can tell you any details? or get in touch with breeder etc? If you have papers, is the breeders name/address not in it. Im not saying that theyll still be at the same address but you could try for nothing