I'd try King Slocombe if I were you - I have no idea about numbers of boys they have, but they have a lot of successful pupils/past pupils, and offer what you want. If you don't like it there you could try Bodyworks. It depends to an extent how serious he is and what sort of standard he is etc.
Hi! We have just moved to the Cambridge area from Boston USA. My eldest DS was in a dance class there for the last 3 years and we want to find somewhere local for him to continue, but somewhere that has boys enrolled! He got tired of being the only one. Preferably somewhere that does ballet and Jazz and modern/street. We are south of Cambridge. THanks all