Honestly there's no easy way to find a good one, it all really depends on how you get on with them personally, one could be great for someone but not right for you an unfortunately you won't know till you meet them
My first was through my gp, she was apparently good I was told but I hated her, she just spoke about how her son done all these things that I should be doing myself, so I then got referred through the NHS an he was amazing, we got on really well but I could only have so many sessions with him because it was the NHS
It won't hurt to try the gp first an see how you get on, but don't feel you need to go back if you don't click with them, it's important to be able to feel comfortable as you won't open up to them if your not, am not sure how long a wait it will be if it's through the gp, I was quite fast but then it's a small enough town that I can get same day appointments, if you feel the gp is too long then maybe look into private but again if you don't click then don't feel you need to see them again, a good therapist won't take offensive to it as they know how important it is for the person to feel comfortable with them an sometimes that's not always the case