GBodyParts.com carries replacement AFTERMARKET AstroRoof seals, but be forewarned. They are of a higher durometer (more firm) than the original GM seals. Unfortunately, the original GM AstroRoof seal is no longer available. You might get lucky and find a NOS one on eBay, but don’t be in a rush. I have a search saved on eBay in case one ever pops up, but it’s been well over a year with nothing.
There is one member on here that has a NOS GM AstroRoof seal, but he’s not willing to part with it unfortunately. 🙁
I bought one of the aftermarket seals and tried it, but because it’s too firm, it won’t compress enough to allow the roof panel to sit flush with the roof when it’s closed. It effectively turns the AstroRoof panel into a very effective swimming pool should it rain. I ended up reusing my 40+ year old seal, and so far so good.
Good luck with attempting to salvage your AstroRoof!