Ok, still waiting for a quote back from China, but thats a big ass order.
Cheapest so far (viable) would be an official richbrook one for about £16 + p&p
Usual colours - Silver, Black, Blue + Red. They would need to be bought in bulk though, so probably just carry Silver and Black to start?
If the China deal goes through, cost would be about £10 each ... but we'll see....