Get hold of Andy out at Inland RV in California. He can hook you up with just about anything.
Some things you might still get from Airstream, out of Jackson Center, OH.
A place I've heard is good is Oasis RV.
And, you can do a google search on vintage airstream parts and several sites will come up. I plan to buy some new Worthington aluminum LP bottles for my own Excella from a place online. I forget the name, but I think it's like vintage trailer parts or something like that. Google will find it for you. They had the best prices on the cylinders.