If anyone finds one, I’m interested in one too not yet explored if a std older steel tank fits from a 620.
The fuel pump flange ( ooh err ) on the bottom of the tank is unique i believe to the later s4r (testa) and the s4rs. Maybe also an airbox clearance issue. Whatever you do, don’t buy a used US made ally tank. It’s well documented on other sites about the issues with quality including threaded holes that should be blind, go all the way through etc. edit, it was a ‘ Legendary’ brand tank with the issues. This might help http://www.ducatimonsterforum.org/index.php?topic=75951.0
Tecknorace in Italy also make them... when the bank account's a bit healthier I'll be looking at something to replace the swollen one on my S2r