It will definitely have to be bodged with non-vacuum parts and some creativity.
The closest match to what you need is called a "U channel gasket", however this situation is a problem because the gasket on your Silver King is flared to a flat T-shape.
I found something on a website for solar panels but it's likely expensive or difficult to order a small quantity. I'm sure there's another place to find it, but just as an example to show it's out there.
https://elastostar.com/products/extruded-rubber-u-channel-manway-seal-gaskets/
I circled the two I saw that might work. Just showing an example. But it seems like U seals and other type stuff are common with windows and door seals, I'd check hardware stores, and maybe a window repair company and see if they could find or fabricate some kind of gasket.
Also "rubber shower door seal" or "rv window seal" in google images seems to find some close matches too.
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