I dont know where you are but here in NY all mental health providers work on all mental disorders including dissociative disorders. they dont break their services down in just working with one mental disorder or the other. doing that here in NY is called Discrimination on the grounds that treatment providers would be turning away someone just because they have a mental disorder..

example - a therapist who works only with those that have borderline, PTSD, and Depression would have to single out /weed out a schizophrenic, just like you would single out / weed out someone who is black, Mexican, Asian, or had a handicap.

here in NY treatment providers take the non discrimination laws that say you can not fire someone from a job, not allow a person in that school or not treat a person for mental and physical health because they have a mental disorder.

your location my take the your locations non discrimination laws as seriously as my state does.

one thing that might help.. instead of asking potential treatment providers if they work with DID, ask if they work with people with PTSD, Dissociation and anxiety. if so they most likely also have DID clients because DID includes these same symptoms.