Online resources for (and mostly by) autistic adults
There are many websites, blogs, and YouTube channels about autism by autistic people. Eventually this page will list many of the more informative ones.
In the meantime, here are some online forums run by and for autistic people.
Featured page: Where to get an ASD evaluation as an adult.
It's not easy to find psychotherapists who are qualified to diagnose autism spectrum disorder, especially in adults.
On the above-linked page is a preliminary list of places where some members of local support groups obtained their diagnoses. Soon this list will be updated to include many more places and, for those already listed, more information about insurance, other reduced-cost options, etc.