People are often surprised how well dogs take to crates. They treat it like their own personal space, their den. Mine love theirs!
For canvas covers, try looking on ebay, I've seen them on there sometimes. If you have any agricultural or dog shows out your way you can try dropping by. There is often vendors at shows that sell or make to order things like that.
Or if you're handy with a sewing machine you can make your own - use rubber backed curtain fabric, and velcro so you can adjust the sides up and down. You'll probably find a pattern online!