Several sources for tanks currently . Indian sub continent made ones are available thru Ziggy on the west coast US .and other dealers . gelomann.de (Christian Henn ) in Germany sells them also , and Reno in the Czech republic . There are also two sources from Poland I believe, Florian in Austria may be able to help.
It would appear that most repro tanks have a tendency to leak between the gas and oil tanks, so test them if possible , and seal the gas tank portion if necessary.
Tim Berry in the UK repairs gas tanks , another English friend recently had a difficult repair carried out By Robin James Restoration , both of these guys seem to do good work .