No reps as far as I know.
Genuines there are plenty.
AP Boutique by Wheellock place at intersection of Orchard and Scotts Road.
Hour Glass, Sincere are all over the place - Lucky Plaza, Takashimaya, Suntec City and more...
For Pre-owned/ BN watches:-
Far East Plaza - 1st floor 'Time..' Something cant remember. They have used and some BNIB Panerais, AP ROOs, IWC BP and a number of Rolexes selection.
2nd or 3rd Floor 'Monster Time' Used watches - Rolexes, Azimuths, PAMs
Another one more in the complex, cant remember the name.
Time Will Tell (if you like PAMs, they have rolexes as well) at Sunshine Plaze; Bencoolen St. That place is a bloody museum with over 30 PAMs on display in their individual boxes. I got to see their PreVendome Slytech there. Awesome watches, awesome people.
Visiotime at Raffles Place - Bosman, the owner, has tons and variety of stuff. APs to IWCs to PAMs to A. Lange & Sohne to Breguet, you name it.
Sorry as for reps, I cant help u there. You have much better luck in HK & China than in Singapore.
Good luck!! Hope you find what you want, and most likely you will get good deals as well.
p/s I'm sure Admin would be more well-versed than me on this one.