I've GS-125 (2008) Each & every part is available at Suzuki outlets .. A Suzuki mechanic at Suzuki U.R told me that the only difference between GS-125 & GS-150 is "Self-Start" (which can also be installed on GS-125 in 5000-6000 rupees) otherwise body & engine parts are same of these two bikes & can be replaced with each other .. As far as speed is concerned .. I'm not sure about pick-up but top-speeds of GS-125/150 are same (105kmph - 110kmph on GPS) .. aur rahi baat Petrol Average ki .. toh obviously GS-125's petrol avg is better than GS-150 bcuz of the difference in "cc's".. Inner-city avg is 42-45km per litre & 50km per litre is easily achievable on highways
Here's a picture of my GS-125
P.S: That Suzuki mechanic also mentioned the reason of discontinuation of GS-125 was that it was same as GS-150 but due to non-availability of "Self-Start" customers preferred GS-150 over GS-125. This product was getting low sales so the Pak Suzuki management decide to discontinue this machine.