The same gas cap was found on dozens of two stroke Suzuki models throughout most of the '70s ( all of the larger TC, TS, T, GT etc that have locking, flip up gas caps )
If you look at the cross reference link below, you can pick any of the models and search for gas caps on ebay etc. if nobody here has on for you: http://www.partzilla.com/parts/detail/suzuki/SP-44200-33011.html