For a very long time the gasket for the Lionel 610-8057-200 Rectangular Smoke Unit has been out of stock.
I did find that they had the 610-8057-230 without the PCB, but the PCB is also out of stock. I ordered a bunch of the smoke unit reservoir (without PCB), first part solved.
I first set about solving the next problem, I laid out a replacement PCB and ordered a bunch. They work great.
DIY Rectangular Smoke Unit Replacement PCB
Sadly, the next hurdle came up. The 610-8057-216 Smoke Gasket has also been out of stock for some time and I ran out of my stock! I had cut a couple out by hand, that's a really tedious job, that's no solution long term! Riding out of the sunset came @AlanRail to the rescue! I sent him the measurements and a sample gasket (my last one). A few days later a little package shows up with this interesting little block in it.
Yep, in that stack is a ton of gaskets for the rectangular smoke unit. The plastic holder is to keep them from curling.
The gaskets are neatly stacked on a perfectly shaped holder to keep them from getting damaged.
I tried a couple out, perfect fit, now I have all the ingredients to assemble and maintain these common smoke units.
Alan said the GlowForge cut these out in about 12 minutes, pretty quick processing! I'm guessing the fancy holder took additional time. 
The astute observer will notice that the fan intake hole is kinda' large. That was by design, occasionally these gaskets warp and hit the impeller, that stops the works! Since there's no reason at all to have gasket above the impeller, I figured I'd leave that out, one less potential issue.
Many thanks to Alan for filling in the final piece of the puzzle! 
