Another source for tires -- perhaps for your Airstream but certainly for that weird little utility trailer out in your shed .......
Northern Tool & Equipment Co. -- 1-800-533-5545 www.northern-online.com
Their catalog lists both an F78 x 14 and an F78 x 15 high speed assembly. They also carry compressors, pumps, pressure washers, jacks, bearings, and other neat handy man stuff.
They also have retail stores about -- Knoxville, Milwaukee or nearby -- etc.
For 23 years I had a Coleman Pop up with 16.5 x 6.5 x 8 tires -- no way you buy those from a tire dealer -- even Sears quit carrying them. But you can get them from Northern. I gave the Coleman to my daughter -- its still going.
Hartwell