Brian
I’ve found a company in Germany who appear to have 71mm Piston rings for the CB1100R/F advertised on their web-site. I don’t read German so its difficult to read but may a German member could help translate.
http://www.scheuerlein-werkzeuge.de/product_info.php?info=p688_honda-cb1100r-kolbenringe—1–uebermass.html
Regards
Trev