Have a look on the BACP website www.itsgoodtotalk.org.uk there's a counselling directory of all types of therapists and an easy search tool. BACP are well a respected organisation and therapists have to jump through hoops to register with them so you can rest assured therapists are thoroughly trained, qualified, insured etc. If you struggle to find what you want, call them, they are helpful and will steer you in the right direction.
Art therapy tends to be good for young children, it's a good way of developing a relationship with the therapist without any pressure, they do things like draw, look at artwork, discuss and the talking evolves naturally from that.
Have you also considered family therapy? It can be helpful for everyone to talk together but it depends on your sons personality and whether he would be able to open up with immediate family members present. The most important thing for him is to be able to speak openly and freely without fear of reprisal or judgement.
It sounds like you are doing the right thing, trying to nip it in the bud and deal with it sooner rather than later. Is he happy at school? OCD and anxiety might be indicative of some issues there. I'm just guessing.
Good luck with it, I hope you find him the help he needs 