The first question—is it still under warranty?
If not, you'll probably have to go through a dealer since Airstream only sells a limited amount of things through the company website store.
But, a local seamstress may be able to help you. We have found seamstresses in different places we have lived who do very good work at reasonable prices. Sometimes you can find them through asking friends and neighbors, or they work through a neighborhood store.
If the tear can't be repaired, consider recovering all of them. Our upholstery was ill-fitting, hard to get clean, unlined, and looked kind of cheap (because it was). One was refitted at the factory under warranty. After 4 years, we decided to get them recovered.
We went to a store that was going out business and got a great deal on good quality vinyl in a color that we really liked. Then we took it all to a local seamstress who worked at a clothing store and would do repairs and recovering on the side at a very, very low price. She did good work too. So we had 6 cushions done for around $100. This would be a hard deal to beat, but you get just what you want. If we didn't get the vinyl at a super discount and the seamstress charged what her work was worth, it might have been $300. Airstream's prices can be so high it might not be a bad idea to get something that looks better and is better. We've always found seamstresses through word of mouth, or some work out a clothing or fabric store.