I looked a few weeks ago, was surprised how little I could find. IIRC the best option was to get a company to make you some bespoke iron-on logos but then you'd be treading into copyright etc...
Might be worth trying one of those crappy T-shirt/hat stalls that have a computer-based sewing machine and seeing if they'd knock you one up.
Cheers Dave, wish you could just buy them off ebay or something.