As a pp mentioned, he would need a trauma informed therapist although I disagree with what that poster has said about nobody with trauma should do counselling. My attempt at trauma focused cbt led to my first suicide attempt and counselling has been a literal life saver.
The cbt therapist was not helpful when the techniques did not work for me. Implied I was not trying hard enough. My counsellor is the one who sat with me while I struggled to get words out and answered my phone call at stupid o clock in the evening during a crisis.
Not everyone is the same.
I'd advise searching a register, COSRT would be best as almost all the therapists on there will have dealt with cases of sexual trauma or you can use the BACP site, which is what I used.
I scanned photos first tbh as anyone who remotely resembled the rapist was a hard no. I filtered for about 30 miles of where I lived as anything further away was hard to get to and then made a shortlist of people I liked the look of, were qualified and that I could afford.
The counsellor I ended up with was actually the least qualified of the list but he called back immediately, was respectful of my space and the fact that I was nervous about going into a house with him.
He kept his hands in his pockets until he sat down, no sudden movements and explained that he would not ask for details but would listen if I wanted to talk about the details. It took me nearly 2 years to do that but I can tell him anything now and I felt safe with him.
Make a shortlist. Go for qualifications, not necessarily modality, I've never really found it mattered, it's more about their style of working but they must have some experience working with trauma. I had one who kept telling me I just needed to write down activities and pull them out of a jar during panic attacks. Loony. She was the trauma cbt specialist as well!
Cost and location are obviously something to look at. Ask him if he has a preference for male or female.
List up to 10 options and let him check it out. Arrange for more than one intro session, meet a couple of them at least and see who he is most comfortable with.