While CB650 SOHC 112 link cam chains are discontinued from Honda, they are available from K&L supply, a company with a great reputation for supplying OEM quality hard parts to dealers and independent shops. After decades of using their parts in dealerships, I have 100% faith in their quality. K&L's part number is 12-0401. It retails for around $100.
The reference number for the chain is 82rh2015 X 112, which is apparently an industrial part number. If you search the 82rh2015 X 112 number, you can find UK and European sellers of that chain specifically for the CB650.
Morse, a division of Borg Warner, is an OEM supplier of cam and primary drive chains to Honda, and may be another source.
