I have meet a few therapists who don't write letters, usually it is out of ignorance. I have read about doctors who prescribe without the letter, they are fine. The letter is just a formality really, meant to protect the doctor at the expense of the TG patient.
I would find another therapist, because it seens to me he would not be willing to refer you for SRS either and I don't think it would hurt to schedule a consultation with one of the doctors he mentioned.