Red,
When I went to the Dayton airshow with the Con attendees in Indy I was totally UNIMPRESSED with the various T-shirts, posters and other "stuff" they had for sale.
If I were you I would use these airshows as a stepping stone to getting your business up and running.
Obviously you will need a bigger portfolio to begin this, but once you have a collection you can:
1. Make frameable prints of the drawings you have done and sell them.
2. Offer commissioned drawings and use testimonials from former customers, such as myself, as proof of your ability, integrity and pride.
I think over a million people flowed through the Dayton show alone....all people who have an affinity for aircraft. It would be a bonanza for you man....guarennfreakinteed.