I think you can get Yokomo/Mugen 1/10 cars and parts from:
1) Pacific Model (Sim Lim Square Basement)
2) Hobby Boom (Excelsior)
They also carry Mugen 1/8 (World Champion). Both are great stores offering very competitive prices.
For US brand: Associated Nitro TC3 (World Champion/TQ '02):
1) Pacific Model (Mugen/Yokomo/Serpent/NTC3)
2) HobbyLink (Mainly Serpent 1/8 & 1/10 and X-Rays EP)
There might be others that I don't know of, so fill in if you can...