Here is a pretty good source if you don't want to pop for the Suzuki part which I have no experience with.
#MP14 30mm x 1.5mm RH External
#MP14 30mm x 1.5mm RH External
Thread Deep Reach GS1100/1150 (81-85)
Note: small diameter rotors on these models
$25.95
This is the same one as my bike.
See related link and post #10 and how I improved the puller
The rotor can still be very difficult to get off as it should have been RED "Locktite"ed on (or using the Suzuki equivalent)
Heat helps alot, but propane has not worked for me . Mapp gas has done the trick. Keep it off the magnets in the rotor. Apparently it takes about 400 degF to melt the RED Locktite.
In addition you still might find that the puller tool will give out (mine did). So I significantly increased it's strength by over sizing the bolt. Not only is the bolt bigger with fine pitch, there are now more threads. The original weak construction only had about 0.5" of thread where with the oversize fine pitch it is closer to 1".
The hardened bolt and drill and tap are common enough, As I recall they cost me about $50, so a trip to a machine shop might be less expensive if you don't already have the stuff.
Also put a little axle grease on the threads, they will thank you.
Pos