Doug, there seems to be a few out there, but it is not an easy search. Some seem to be overpriced. I just purchased a 2004 30 ft w/slide. It was low mileage and seems to be in good shape.
One thing I was alerted to was to be aware of the possibility of water leaks, especially from gaps in the caulked areas between the front and rear caps and the roof. A leak at the rear can show up in the rear storage compartment.
I have seen a case of delamination on the sidewalls. Not sure what is the cause or fix for this problem.
As far as I know, the 2004 and 2005 used the same Workhorse chassis, 8.1 l GM gas engine, and Allison transmission.
I found the NADA RV guide to be a fairly accurate guide to Airstream motor home prices.
Keep us posted on your search and progress.