If I am reading correctly, the original owners weren't the ones who bred her to the stallion, but the in between owners? And the "in between owners" who were neglectful of the stally, and who bred mares on their property do not want to be tracked down, because they know if they were to be found they could poss. Be in trouble with the law for neglect of animals, and now you are stuck because if they gave you the signature for the registration papers you'd gladly leave them alone, but they are buttheads so they refuse to reappear.
And now your foal hurt himself. Oh man! You are having a terrible time of it :( I'm sorry, I have no clue how to help you, I have just been following this thread to see what happens, but I feel bad for you! Hugs!
"There is no purer love than the love of an animal"