I agree with packrat Sunbrella is one of the best, however it is not the only fabric for EVERY application, there are other good fabrics. Try
http://www.marinecanvas.com/ to find a qualified local fabricator.
You should look for a fabric that carries a minimum of 5 year guarantee. And avoid anything with cotton in it (like the cheap gray covers)
It will certainly cost a little more to use a custom shop, but the end result should be worth the investment.