Thanks for the suggestions, and let me address them. I live in Portland, OR. None of the upholstery shops or canvas suppliers here have it. Sunbrella, being a synthetic, will not, in my experience, stretch properly; i.e., like cotton duck; nor does it look quite right to me. And dying the natural canvas presents problems of consistent color. For a show car this just won't do. Defender does not offer a black.
I did find a sailmaker in Portland who had #8 black canvas, and I will go see him tomorrow; but it sounds from his description like a double thickness fabric, and how that will stretch remains to be seen.
Thanks again for your suggestions. Anyone else have an idea?