The original Regulator is long gone I'm afraid, it hasn't been available for some years now. What you would need to do is install a universal regulator but there would be some modifications you'd have to make, mostly having to do with plumbing parts and fitting.

On www.mastertoolrepair.com you can find some Regulators that may work for you, like the "REG0250M" which is a very popular in-line type of Regulator.

Any Regulator you install will, of course, require some mods as anything you use would be a work-around essentially. You can probably just install a pipe nipple into the inlet of the Manifold where you original Regulator is now, and simply use the REG0250M which threads onto a 1/4" pipe nipple, and thread a pressure gauge into the side of the new regulator, and your Coupler to your hose screwed into the Outlet of the Regulator body.

Hope this helps!
- MTR