without switching to chain drive i think the stock wheels are your best bet. Look on ebay if you need/want stock replacements. they can be had quite cheap. There isnt anything aftermarket that isnt ungodly expensive. In fact the aftermarket wheels I have seen were probably one shot custom made. You could go to a bike salvage or junk yard and do a bunch of measuring of wheels from different bikes to see what'll fit but then the issue goes back to the chain drive conversion. '83-'86 gs550 CAST wheels work with minor spacing changes so i would imagine the 550 spoked wheels will aswell but I'm not certain and...chain drive.