I want to rephrase my initial answer - there are some, but I don't think there are enough locally to me. My mum's old horse was an ex-riding for the disabled pony and my friend recently sold her horse to a riding school that caters to those with disabilities. That being said, I feel that it should be more accessible, instead of a select few specialist riding schools.
I absolutely love what you are doing and striving towards! My mom works as a registered hippotherapist, which means that she does therapy for children when they are riding. I don’t know of any shows that include disabled riders but I hope that you will become a barn that supports that
At my barn in Finland there’s lessons for people with disabilities every Friday and sometimes individual lessons on other days too. I think it’s really great that a normal riding school can offer a thing like that!