Bill,
The boat shop may have the material you need. Boat covers and awnings for buildings are usually made from Sunbrella. Another older name, which may not be around any more, was Acrylon. Boat cover shops and awning shops should be able to get what you need. If you have a color other than black you will need to compare a swatch to your existing material. BTW the stuff last for a long time. I have a cover on my boat made from Acrylon that has been out in the sun every minute of it's life which is nearly 20 years. I had to have it restiched once about 10 years ago, but the material is still in decent shape.