Watch ebay. But honestly I wont use a stock cylinder stud even on a stock motor, they stretch too easy and one of the reasons the head gaskets seep. They stretch even under stock loads. Aftermarket heavy duty studs are the only option in my opinion, not worth even thinking about using stock studs.
I have the set that I pulled from my 75 CB750K when I rebuilt the motor, I replaced them with the APE Studs as dirtdigger suggested. From what I've read the stock studs do stretch and raplacing them is suggested. https://www.z1enterprises.com/product/APCS750H