Learthman: "where can I buy this"? What is the "this" you are referring to? All you need is the gaskets from Vintage trailer gaskets (They are very helpful) and from what I see the "Airstream
1966 to 1984 vinyl glazing for 1/8" glass" is what you would need. And at $0.95 a foot, that's not a bad price. I think it comes to roughly 7 or 8 ft per window. Be sure and by extra.
Feel free to send me a private message and we can exchange emails or phone numbers, if that makes it easier.