When I replaced the canvas on my Junior, I used Sunbrella that I sourced from a local
awning shop and put screen openings in using normal
fiberglass window screen. For the foam cushions, since there's nothing special about the shape, I went to a local foam/upholstery shop and talked to them about the various qualities and durabilities of foam and had them cut me the large rectangles. I sewed mock-box covers out of upholstery material I found on sale.