Impossible to suggest suppliers without some idea of your whereabouts
Perhaps the folks at
fastlane would be a better place to ask, drop-tanks not being real crowd-pleasers in the FE-FC area. (This is a forum for FE/FC Holden enthusiasts, after all). Also, a look through the advertisements in Street Machine or Cruzin magazines could be useful.
Failing that, have a look in your local Yellow Pages. I'd start with Radiator Repair and LPG Conversion places, both of which have an interest in fuel tanks and related items. They might be able to put you onto a local supplier.
cheers
RET