Well, obvioiusly any other Airstream (or SOB, for that matter) window will be perfectly suited to be a donor window. I'm thinking specifically of Craig Dorsey of Vintage Vacations, who was interviewed on on the show "RV Today".
He said that for actor Billy Campbell's custom 50's Silver Streak trailer, he added like 6 or 8 skylights throughout, by cutting down curved 70's Airstream windows to be long and thin. The effect was almost like the ceiling of a yacht's cabin, small rectangular skylights with rounded edges. It's something I'd like to do with our Globe Trotter as well - we'll see.
As we progress, I'm considering the porthole-in-the-door idea as well, which Dorsey also installed on a '61 Globe Trotter recently. That one is pictured on his site, and perhaps he'd tell you where he found it. I like it because it has frosted glass, removing the need for a tiny curtain in order to get privacy.