Okay, just found this and haven’t scrolled far enough to see if anyone’s answered - it might be time consuming but maybe poke around race charts on equibase and look at owners/breeders in races your horse ran in (or races held roughly the same time) I think I found a few others that were connected to where my OTTB was bred that way. Again though, that’s time consuming and you might not find anything.
Oops just realized that post was YEARS old sorry.
EDIT: Oh and don’t give up either - I found the full sister to my OTTB (he died in 2013) like, totally randomly looong after she left the track (my boy was foaled in '04, she was foaled in '03, my boy raced '07 and '08, she raced I think '05 to '07) via a Facebook group called OTTB connect when I searched her registered name and found someone who’d posted her name in a thread of strange/dumb/funny JC names they’d seen. DM’ed them (they’d mentioned in the comment that was their mare’s registered name) and asked if (Mare’s name) was the one foaled in (state) in 2003 by (sire) out of (dam), b/c if so I had owned their mare’s full brother once he retired. Yup. It was her. I’ve got pics of her now too and there’s SUCH a resemblance (except my boy’s sister would be a full hand shorter than he was, my boy was 16.3, his sister is 15.3) and she apparently was a pretty decent low-level jumper for a while (I had always wanted to do jumping or eventing with my boy but he died before we really had the chance so it was nice to see his sister had talent - maybe a little bittersweet as I wonder what he could’ve been, but still nice).
