You should be able to find metric allen screws at a decent hardware store - the Ace hardware stores around here carry them. Unless you foresee doing a lot of piping work, I'd suggest reinstalling the pipe jaws as is.
I've had a couple of that general style vises over the years, and they are handy for light to medium work. Don't use the anvil (or any part of that vise) for serious pounding.
As you can see in scratches in the paint, that vise has had bondo applied to smooth out casting flaws and roughness. This was common in the early era of that style Asian vise. Some folks have stripped off the bondo to repaint and wished they hadn't.
I'd suggest (1) judicious use of a fine wire wheel to remove the rust on machined surfaces; (2) clean off all of the old grease, swarf, and muck; (3) regrease with a good synthetic grease (Mobil 1 or similar); and (4) reassemble and put it to work on your workbench.
IMO it is hard to justify a full restore/repaint for that vise, but if you choose to repaint, be aware of the bondo issue. In your last pic above, you can see the bondo in the large scratch, as well as cracks forming in the bondo.
Use it until you run across a smoking deal on a Reed/Wilton/Athol/Rock Island/Parker/ etc., then do your full restore.