Call a motorcycle junkyard and see if they've got any 1980-82 CB750K's with complete wheels, and be prepared to make them look pretty. Trawl Ebay too and set up search alerts for when new listings pop up.
Or you find the bare hubs (Ebay or junkyards again) and build up the wheels yourself because VintageCB750 sells new OEM rims and replacement cad-plated spokes.
It took me a while to find a solution for my own 1980 K's rusty rear rim. I ended up nabbing a used rear wheel from a 1981 on Ebay the same day it was listed and rebuilt it myself with new spokes. I went from a 17 inch with a ton of flaked chrome to an 18 inch with almost all its chrome intact.
Wheelbuilding isn't a dark art, but it is tedious and requires plenty of patience.