To my knowledge, the special plastic drain pan is custom fit to the Dometic Penguin models. It does have a curve to match the curve of the roof, but the curve is more about aesthetics than function (ie., you don't need to have the pan in place to fit an AC to the roof of your trailer--it is just there to catch condensate). If it works with other brands it would be pure serendipity. The thing that makes the pan specialized to the Penguin is that it is the exact size of the bottom of the Penguin, so the AC sits down into the pan without leaving any gap around it, and it has channels built into it that catch the water that drips out of the drain holes in the AC unit and channels it into the drain tube. If the condensate drip holes in your AC are in a different place than on the Penguin, or if it has different dimensions, then it isn't going to work.
There is a kit available from suppliers like outofdoorsmart.com that just looks like a couple of plastic cups and some drain hose. This is a system that a lot of folks are going to instead of using the pan. Basically, you use a double thickness of foam gasket between the AC and the roof, and you install the cups under each drip hole on the AC, and then run the drain tube through the foam gaskets and into the trailer where it connects up with the condensate drain line in the wall. This kit should work with any AC, and is not really model specific. Again, you don't need anything to adapt the flat bottom of the AC to the curved roof of your trailer--the foam gaskets will do that job.
The only Airstream guy I am aware of in your area is Frank Yansen, but I would imagine any RV shop worth its snuff could do the job.