Try Vintage Trailer Supply (google it for the exact website). I got a roll of the large "T" seal for the top for under $20. Enough for all the windows
on my 1300. Beware...there is a detent in the track (sorta like a machine - punched dimple) that makes it difficult to thread the new stuff in. Use lots of soapy water as a lube.
If you are resealing because of water leaks
, check the seal around the windows first, After about 30 years the butyl rubber sealant has hardened and cracked allowing water in. Lots of info on this site for the re & re job of resealing.
All my other rubber seals are original and, although not as flexible as new, still seal OK.