Oh, that's right. Its THAT one. Nope. No good. Too dangerous to use and may explode upon opening. Better box it up and send it to me
I'll dispose of it nice and proper.
Seriously, if you are a solo diver like your tag implies, you realize there are risks associated with our sport and maybe displaying that reg is all you should do with it.
Me? Well I searched a few places and found hoses, gaskets and such for mine. I didn't need a diaphragm but new silicone ones are available. If you don't feel comfortable opening it and peeking in, then maybe you should sell it and find a USD or Voit. There is a much better chance of finding parts.
But before you do, ask yourself what exactly do you intend to do with this vintage gear of yours. Will learn to dive it? Where? Inside the Oriskany? or in a pool at 6'? On a sunny reef at 3 fathoms? I wouldn't be scared of learning from this early dual hose regulator. Just realize you have limitations with this one.