How can I find "free-lance" therapists for a Down Syndrome child?

Start in the Yellow-Pages for Occupational, Speech and Physical Therapists in Private Practice. You could also Google: Occupational Therapy Association (for example) to find professional sites that will have member directories.

If he is progressing very little, he may be in the wrong educational placement and may need more or different services. At the next Individualized Education Plan (IEP) meeting, his parents will want to bring up those concerns and discuss other options. The school district is required to provide all the services that he needs; you shouldn’t need to pay out of pocket for it. Convincing the school district is often not easy as providing these services is costly. If they balk, I would suggest contacting the local Education Law non-profit.