I have a 64 Safari with the "Door Within a Door". I have found gasket/weather stripping from 2 places that work.
1- (VTS) Vintage Trailer Supply - https://vintagetrailersupply.com/
2- Vintage Trailer Gaskets. https://www.vintagetrailergaskets.com/
They both have similar products, but different manufacturers. They will both send you samples to try. VTS charges for there samples, Vintage trailer gaskets did not charge me for there samples. I have used both sources for my windows and door.
P.S. No one makes the exact gaskets that came stock on these years. You will have to take measurements and use the size and style that will work in your application.
For example, I used the MED. D-seal 1/2" wide x 3/8" tall from VTS for the inside door within a door gasket.
Hope that helps,