Hello Judy -- and welcome to the Forums! I do not think there is enough of a market to bring anybody into the business of building Airstream cabinets or shower enclosures on speculation. Fragmenting the potential further, Airstream has gradually changed roof contours over the years. That leaves your own skills or else hiring a custom restorer for high-spensive prices.
You may find some general RV items that would work (I wouldn't speculate what that would be) -- but you'll have to be just as lightweight as Airstream was originally. There are so many structural, plumbing and electrical jobs to take on that I'd say most folks leave the cabinetry original. Now and then somebody else guts an Airstream and puts notice here about availability of something they didn't want.
You will be luckier with a toilet. See
http://www.campingworld.com/ under Sanitation.
Best of luck!