Well, there's a few routes to go. You've no primary doctor, and are aware of it, so there's not much point in going into it in detail. However, GPs sometimes will prescribe and monitor the initial steps instead of just referring you to a psychiatrist.
Which is where you'll end up, eventually. Either directly, or via a PA or other mid level provider under one's supervision.
Depending on how you're paying for it, you may not need a referral anyway. Just a reference, as in someone, anyone, who knows the local options and can point you to psychiatrists nearby. A therapist should be able to do that just as easily as a GP.
You can try community clinics as well, particularly the ones that provide a range of mental health services. They always know what doctors are out there, and sometimes have one.