I will gladly settle for a semi :^D but for the reasons that you stated, I doubt that we are going to have access to any.
At what point does a weapon become illegal?
Are cannons and such allowed?
I know that "historical" artillery is legal, like muzzle loading cannons used in civil war demonstrations. I believe that the maximum bore size for "modern" firearms and such is 20mm. Of course, I could be wrong, but I do know that you used to be able to legally buy 20mm anti-tank "rifles."
Mark