In reply to girlymonkey:
That is a pretty narrow-minded response...It costs nothing to try and it's not that long ago that there wasn't mens or womens specific harnesses (or other equipment!).
My suggestion is based on the fact that the OP has tried womens harnesses already, is finding that large isn't large enough, and presumably running out of options (hence asking). A large mens will tend to be bigger than a womens large so has to be worth a go. I've fitted harnesses, and shopped for harnesses, for women so have an idea of the difficulties faced (including, seeing as we are making sweeping statements, how colour is more important than fit).
As I say, it costs nothing to try and they might find a harness that fits.
(PS - in my experience this also applies to footwear and various other items of clothing).