Unfortunately the window part you're looking for is NOT readily available anywhere that I've been able to find. About the only option I can think of would be to remove one from another window and take it to a fab shop and have them make you one or two replacements. If you do that go ahead and have one made for me!
Air forums # 1674
1974 20' Argosy Motor Home
1974 31' Excella trailer (parting out, as of 4/1/2015 I have wheels, brake drums, windows & holding tanks left to sell)