Racks for any of our old bikes are very hard to come by. I got into an Ebay dog fight on a bid for one for my CL100 a while back but my wallet ran out of airspeed, altitude and ideas passing through $220. Since then, I have settled into using a magnetic fuel tank bag to carry small items, bike documents, etc.
I would suggest using a perpetual Ebay search and one will turn up eventually. Just be prepared to pay dearly for it. You can also check the For Sale ads at the Vintage Japanese Motorcycle Owners Group and post a Wanted ad there as well.
Rick