It depends upon what you are looking for, and just what you would consider a "model". Hot Wheels has produced at least two "collectors" edition models with a tow vehicle towing an Airstream. The earlier model is a Cadillac "woody" hearse towing what I believe has been described as a 1950s Flying Cloud - - it is called the Airstream Dream Vehicle Set and has an SKU of 0-74299-29216-3. The more recent (and somewhat smaller scale) set is the Hemmings Motor News tow vehicle (1956 Ford Pickup Truck) towing a 1949 Airstream Clipper - - it is described as the Hemmings Motor News collector set - - and it has an SKU of 0-74299-57264-7.
I also have a 1/64th (?) scale model of a late 1950s Flying Cloud that I purchase from an E-Bay Vendor about 12-months ago that is quite well made, and has very realistic detail. It did not come in its original packaging nor are there any maker's marks on the unit so can't provide much more information on its origin.
Good luck with your search!
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)