First, it's best to check the ISST-D members list (http://www.isst-d.org/). Unfortunately, there was no one reasonably near (considering it will be a weekly trip for a long period, I'd rather have it not too far away). They are (AFAIK) all experienced with dissociative disorders and trauma.
Then, I started at a random therapist (doesn't matter much which) and looked for a psychiatry association (I guess that's what it's called in English?).
If you're lucky, they have a list of members, searchable by profession and location. If you're really lucky, you can include dissociative disorders and sort at distance. I wasn't very lucky. I went for 'emdr' (there wasn't even trauma in the list, but I guess emdr covers that

Next step will be actually contacting them in some way. Think I'll post when I've done that (and how). I think I'll ask whether they have any experience with dissociative disorders (considering I've been diagnosed with DDNOS, so I have 'proof') and autism (probably not very relevant for many forum members, but it is relevant for me). The latter is not a requirement, rather 'good to have'.
I made this (general) thread to share tips/ideas on how to find a therapist. Feel free to share your tips/advice as well.