If you could get a kind-hearted judge involved, you could run a show or series of shows where the entry fees went towards the program.
Also, you could do an open house to encourage visitors and hopefully donors? Could include a fundraiser BBQ, pony rides, lesson demos, tours, etc. You could even combine this with the horse show/s.
A therapeutic center near me does a show yearly, not so much to raise money, but more to show off how fantastically their students are doing. Many people show up and are often amazed at what the program provides.