I've been there; the irony is that the resource you're looking for is people. Find & join your local autistic community (the actually autistic people, not the moms or professionals); they know where to get a diagnosis.
It's ironic because it's an autism thing to consult websites, books, etc., but not other people.
Choosing from the group of people who have been diagnosed to see who they can recommend to examine you... you realize that this is the worst form of selection bias, right?
The reality of seeking diagnosis as an adult is that you get endlessly dismissed. I've been told I can't possibly be autistic because I can make eye contact, can talk, drive a car, or get to the appointment by myself. I've been misdiagnosed with and medicated for ADHD, personality disorders & OCD. The blatant incompetence of mental health professionals and complete lack of proper support and understanding drove me to the brink of suicide. So... yes, it's a bit of a selection bias, but the other option of searching at random - and getting hurt along the way - is just hell.
False positives are rare and inconsequential; false negatives destroy lives. It's as simple as that.
It's ironic because it's an autism thing to consult websites, books, etc., but not other people.