Probably true on availability, a lot of stuff is unobtainable right now,
I am considering getting one off of that auction site, there are decent
ones from time to time. However, almost always listed as "has cracks",
if not all the way through (like mine is) I may try to get as decent one
as possible, and perhaps coat it with an epoxy to get the most miles
i can out of it...
Has to be a common problem for a lot of us ?

mmmh, there are reproductions available with better rubber and you want to purchase another 45 years old intake with less cracks and hope to repair it with epoxy?
All those intakes most likely lost their flexibility. Between barrel and carb, there are vibrations and heat. The repair would be 2nd best option after a reproduction. 

 No, I didn't want to purchase a used one, but I'm not restoring it, I'm riding it. Budget is a concern with the number of toys to keep on the road, whether 4 wheels or 2. I've purchased a very nice used one off the bay. Doesn't appear to need epoxy...mating surface to head looks good.I'm guessing it will still be more than usable long after I'm gone !I've also got a rebuild kit for the carb, which I intend to do at the same time, of course, that I replace the manifold. There is an occasional overflow issue, so that will get remedied. Then all will be good to go ! It's incredible some of the pricing for parts, as is the case for the manifold, be it used, or reproduction, let alone bikes....I rode mine to work a few days ago and had 2 people ask me if wanted to sell it...I knew the one guy, and I know he could well afford it if I named my price, but, I said, "not today" !It's still way too much fun to ride to put a price on it ..Thanks for the input.
daily