Indeed there are heaps!
Not much in Singapore, given Singapore doesn't have *mountains* just *hills*.
However, still enough to keep you entertained. And people go off one-day trip to Malaysia, nearby Thailand, plenty of spots!!!
As for bike shops
www.togoparts.com (all directories are there)
if you want t know more about singapore mountain biking see below. There are again so many mountain bike groups, they organise leisure rides, competitive rides, night rides.
Singapore Mountain Bike Forum Intro
www.smbf.com.sg