It may depend on where you are. In semi-rural Pennsylvania, all the therapists specializing in children with special needs work through the government or through private schools. My brother is fortunate to be able to attend a private school for kids with disabilities and his tuition is paid by the school district as it is cheaper for them than mainstreaming him.
When my mother wanted different approachs for speech therapy than the therapist was willing to try, when my brother was a toddler, the only help she could find was a group of mothers studying some techniques on their own and getting private consultations from a doctor who donated his time to help them out. It worked out ok but the lack of private-market services was amazing.
You may be right in a rural area that there aren’t therappist in that area because they don’t have enough clients, but in the cities there are lots of private therapist.