That's a good question. The Gen I bikes had an optional heated grip kit - p/n 23P-H29A0-V0-00 and I'm not sure if the dealer can order parts for that kit or not. I can't find any individual part break down for that kit.
The Gen I kits had a three terminal plug, IIRC. The Gen II kits which can be ordered individually since they were not an accessory, but an included item on ES bikes, have individual two pin plugs. But I've never seen the Gen I kit since I just used Sympatex heated panels on my own grips and a Heat Troller to control them.
Question for the OP - Do you have the Yamaha accessory kit? Big round knob controller that says Yamaha on it and is usually mounted off the left grip or mirror bolt?
And does anyone know if that controller is picky about ohms resistance in the heating elements? The Gen II kits are controlled thru the ECU, so have to be a specific low ohm resistance. Because the Gen I controller is just a plain device, it may not be so picky.
I happen to have a Honda factory right grip heater unit, new with box and instructions plus some wiring. No controller or throttle tube. It measures just over 1" ID, so will fit over any standard throttle tube. This is the same style as the Gen I bikes use with a remote control mounted with the grips. You may need to splice some wires or make an adapter, but it would otherwise plug right in and just work. $45 shipped to your door if you want it. PM if you have questions or want pics.