If you wanted to construct a new line with rubber vacuum hose you need to save the end fittings and nuts. Check valves can be had as in the attached picture or they have plastic ones. EBay and Amazon sell them.

You will have to find something that works for the little nipples to T into the main line. It could be done with Brass fittings.

I replaced the plastic tubing on my Power Brake Booster Vacuum Line with rubber vacuum hose. I increased the length so I could run the line over the top of the fender well were it was less likely to be damaged.

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84 300D, 82 Volvo 244Gl Diesel

This sounds like great advice and a good solution. The phrase "necessity is the mother of invention" comes to mind. Really does suck when these parts just go "NLA" with no warning or recourse.
I, too, just bought one for my 83 240D from PP "not too long ago", as well.
I was recently looking for an ac line for my 97 E300D, guess what? NLA. It's the main low pressure line from the compressor to evaporator with the "low side" charge port in the middle. I found one on eBay from Germany, for $20!!!, but the guy wouldn't ship to the U.S. The new part from MB was over $300. Not having much luck.
My local dealer kindly did a "national search" of all the MB dealers, hoping to locate the line in someones parts dept.(no bueno). I wondered if you could get a dealer to perform that same search for your brake booster line? Surely, there's gotta be a new (or used) one of those, somewhere on this planet, yes?
I know there are also a lot of members here who also stock up on old parts. Have you tried placing a request in the "wanted" section?