Just got back from Goa on Monday.
Finding somewhere that hires bikes legally shouldn't be a problem. I really wanted to hire a Royal Enfield but because I was on a family holiday, I decided against it. OK, I admit it, the girlfriend said no after seeing traffic in Calangute
Most common bikes seem to be Honda Activa scooters, Yamaha RX100 and what appears to be a Honda CG125 but with a C90 type engine.
Also quite a few small engined Fazer and FZ lookalikes. Spoke to one of the locals who asked me what engines and power outputs Fazers in the UK had. You should have seen the look on his face when I told him!
The traffic is a chaotic compared to Europe and its not just the locals. Some of the tourists on bikes are nothing short of incompetent by any countries standards.
Hope it's not anyone here but I did see the English driver of a 4x4 re-pass a local on a scooter who had overtaken him and then deliberately open the drivers door into the riders path then shouting a load of abuse at him. If it is someone here, you're a muppet.