You may want to call area horse rescues, as they are familiar with abandonment situations. If they can't help you directly, they can probably direct you to a lawyer locally who has experience with the topic. Depending on how good your Animal Control officer is, he/she may also be able to steer you in the right direction.
I 2nd Kate - I have known her personally for several years and my husband who's accounting firm works with Kate has nothing but positive things to say about her. With Equine Issues, Kate would be the ONLY person I would work with, unequivatably.