I don't think the G650GS was ever shipped with wire wheels which might explain why you haven't found any. However, I suspect the F650GS wire wheels may fit. Also, my Aprilia Pegaso had very similar wheels although it didn't have ABS and it had a mechanical speedo drive on the front wheel spindle. The ABS reluctors would probably transfer but you would need a wheel spacer to replace the speedo drive.
Maybe trawling through part numbers on RealOEM might give you some idea but anyway, you've done the right thing by posting this enquiry and you may find somebody with a definitive answer or even beteeer, find somebody who might want to do a straight swap!