Generally the shops are located at the Middle Rd area in buildings like The Bencoolen n Sim Lim Square. As for having a mkt, I'm not too sure as casio buyers here are predominately the younger n fashionable set. But having said that I'm pretty sure there's an underground movement of some sorts...
I prefer the 6300 as it's a really nice weight on my wrist compared to newer frogs!
Yes in a way living here in Singapore we get to see quite a bit of the newer as well as rarer shocks, at a fairly decent price compared to the rest of the world !
Cheers