For the authentic Gibson 335s, go to Guitar Gallery at Parklane Shopping Center. For Epiphones, try Swee Lee and either Bras Besar or Sims Drive.
Yamahas are only found at Yamaha shops. (i.e Plaza Singapura)
You could try looking at G77 at Peninsular Plaza for Tokai, Heritage ones...
Oh yeah... And Guitar Connection for blemish stock