Call for Artists, Making Money at Juried Art Fairs, Craft Shows and Festivals
I get banners from Oriental Trading Company. They are vinyl and cheap!
Vista Print - I have had great success with their banners.
You might also check out shortrunposters.com
Any local print shop will do the job gladly. A place you can order cheap business cards, things like this. It'll be cheaper and faster than any online orders, and people there usually are very helpfull. If you bring a sample design, they will be able to do whatever you want.
My latest banner that I purchased is from Empire banners based in New york. The printing is a good quality, and the prices are very affordable. a 1'x9' banner is listed as costing just over $20. I have no complaints, particularly with how they will put in grommets and pockets for hanging wherever you want.