You could try Jas. Townsend & Son online. They sell clothing for people in Revolutionary groups. They may also have some canvas for repairing the tents.

Thank you all for the links. Maybe one of them will be what I am looking for :)
And debbieumphress thank you so much for the offer. Unfortunately I live in WA state :( But the thought was very kind.

I use 100% cotton duck canvas to make my portable ironing board. I love that it shrinks because I can cover the board then spray with water and let dry. The canvas shrinks to a tight fit. I bought it at Walmart a few years ago. It's very thick and stiff. I have some left if you want this type.