I emailed. I do better in writing than verbally. The first time I looked for a therapist I shared a lot about myself and my situation in the emails I sent out, which I regretted, because on the occasions I heard nothing back, I felt like I had just sent all my personal problems "out there" without knowing who might see it.
The second time around I just said I wanted an appointment for therapy and asked whether there were any weekly slots available. (Most of the info about his practice was available on his website).
This was much better as I was able to share stuff with him at a pace that suited me.
If you are looking for someone with a specific specialism, it may be worth mentioning that in the email; some therapists might be able to point you in the right direction even if they can't help you directly.