I just love this bike.
Yamaha RX-100 has been discontinued since a long time and it is not available in any of the Yamaha showroom. It could only be bought from the used motorcycle market or you can consider the new Yamaha Saluto RX 110 with the same moniker. It is not as fast as the RX100 but carries the same moniker from the classic bike. RX100 was powered by a 2-stroke engine that was good for 11 BHP and 10.39 Nm of torque. It claimed a top speed of 100 kmph and was extremely lightweight at just 103 kg. You can find one on OLX or Quickr.
Know more about RX 100 here – http://autos.maxabout.com/bikes/yamaha/rx/rx-100