Just to more specific, contact your home school (the school that your children are supposed to attend in your neighborhood) and they will be able to direct you to the right people concerning special education evaluations. If you believe it or not, don't take it too hard when they give you a harsh "diagnosis" - the worse label they give him, the more services he will receive. On the other hand, you as the parent know best on what your child needs, so when they offer you their professional advice, ask for OPTIONS and TRUST your instincts. It's going to be confusing at first so don't hesitate to reach out and ask for more advice from other moms.
I have a 6 yr old daughter who we had evaluated at 4 yrs old - we felt that she wasn't autistic but that she still had special needs. We fought the autistic label and settled for the Developmental Delay (DD) label - less services but more appropriate for her needs. Our concern is that she would be placed in a lower functioning class. She is now a first grader who is in a typical (general ed) class and surviving very well with support from us at home and also minimum support from the school's special ed teacher. I also have a 3 yr old boy who is definitely autistic - at the moment, we have school district as well as Regional Center services. After what we went through with our daughter, we were old pros by the time my son came along, and it served us well.
Hopefully, your son doesn't have AS - but if it turns out that he does, there are plenty of help and support all around. Don't hesitate to ask.