The majority of UK glamour models are white, and probably the majority of them are blondes too.
Unfortunately that's just the way it is. You could try sending pictures to Girl Management, Samantha Bond or maybe IMM, but I don't see many black faces on their boards.
Any other 'agencies' who claim to have an interest in you are most probably just trying to rip you off.
I don't know any UK magazines that primarily feature black glamour models - there isn't much of an 'urban' or 'asset' modelling scene here.
Just my $0.02