Prices for Pentax items are about the same in most local shops, and they are about the same comparing w/ other countries. So we won't be able to help you find great deals. But you are welcome to SG and hope you enjoy staying here
If you just want to look for Pentax stuff, you can check out Cathay Photo at Pennisula Plaza around Cityhall area. It's at our city center, so you'd most likely be there anyway.