We used an au pair agency that claims to specialize in it. It was a huge disaster - it became apparent that our so called special needs au pair not only didn’t have any special needs experience but really didn’t have any childcare experience. We never got back the 5 figure placement expenses. I know people will jump on me and say why did we have an aunpair, but this agency promised the world, and with a special needs child and other children, we needed particular hours that we couldn’t get from a regular nanny.
Where we have had luck is asking at the hospital (NICU and picu nurses have had great leads) and from all of the therapists and heads of the therapy places. Generally there are rules about anyone on her case working for us outside of the therapy places, but they have been happy to suggest other therapists who are looking for other hours. Not ideal bc one or two full time would be easier but I’ve been able to cobble together essentially full time care. Good luck. It’s so hard and so expensive.