Which specialists can test for neurological autoantibodies(anti-nmda, anti-ampa...etc.)? rheumatologist? my neurologist didn't know much about it.

For some...: ...Of these autoantibodies, standardized lab tests exist; others can only be identified in a research-oriented institution, as part of an experimental protocol. If the symptoms are bad enough, there is a procedure called plasmapheresis - if there is an improvement after that, autoimmune disease becomes a possibility.

Not a rheumatologist: Nmda is a marker for a type of encephalitis and ampa is another autoantibody seen in encephalitis, ataxia and certain forms of epilepsy. These are not rheumatologic issues. See another neurologist if your current one is not helpful.

A few: There are a few neurologists who specialize in autoimmune neurologic diseases. They are quite rare, and at major centers (e.g., mayo clinic has exactly one who does this). Anyone can order the blood tests. It's knowing which ones to order and whether the symptoms fit any pattern.