Motor Bikes Shops In Bkk

I have done a search a search and located the major motor cycle shops in BKK. Of interest are large 500cc and up machines, not cafe racer styles.

Then i tried to find the locations on a street map. So i know roughly where to start looking. This is where the problems start not the best map?. No help at all.

Can any body suggest/ ideas for the best areas, or major street names (Rama4,5,6), etc to start my search. Perhaps near the sky train or bus routes as i will be on foot. Or try asking a m/c taxi driver.

Any advice would be great