Since they are long gone, or so I've heard, I doubt you'll find a base that will just screw right on as they probably used their own screw pattern and base. More than likely your best option is to just have a gunsmith or machinist drill and tap new holes where you want them for a standard TC base, and use filler screws in any old holes that show.
Location of the rear sight/scope base on standard TC Contender barrels depends on if its a pistol or carbine length barrel. Pistols are back over the chamber, the carbine barrels forward (and maybe the Super 16's as well). I like them back, so even on my custom carbine barrels the base is over the chamber.