A Question About Old car Restoration: Where Do You Get Rubber parts?

I was checking out some vintage cars at a local auto meet-and saw a really nice 1955 Hudson Hornet.
the car was in great shape-except that the windo0w and door gaskets had all rotted away.
Which leads to my question: I recall that big suppliers (like JC Whitney) used to supply these gasket sets for old cars-but they discontinued this over 10 years ago.
So where does one obtain such parts? Unless you were to find some vintage stock (which was stored so that it didn’t rot away)-what do you do?
Can gaskets be custom made?
Given the fact that a 56 year old car used a lot of gaskets, is restoring these cars becoming impossible?

It’s been a while since I restored a car, but here goes:

There are several suppliers of rubber for old cars. Lynne Steele is a big one, and Googling “old car rubber” will give you others.

A lot of the rubber on old cars is standard cross-sections, used on many makes; for instance, the fuzzy strips used at the base of the roll-up-and-down door windows, and the channels the windows slide up and down in are pretty common.

And sometimes you can adapt stuff. I was able to adapt 1948 Plymouth vent window seals to my 1941 with a few minutes work with a scalpel and superglue.

That said, sometimes you’re just out of luck. Or the available replacement rubber is not very good. The replacement convertible top seal I bought for my old Rambler wasn’t quite right–but it was better than the old one, so I used it. The top leaked a little in the rain, but it was garaged inside and when I did get caught in the rain, I was willing to do a little towel work; given the usage of the car, the rubber was good enough.

Metro Moulded Parts in Minneapolis has a large catalog of seals and such. Also they will make custom seals and parts if you just can’t find it anywhere else. I have never bought any retro automobile seals from them, but have used them for the low volume production of custom seals for industrial equipment. Their quality was top notch.