[villagetinker]

Try a Google search, when I was back up North, I was able to find a replacement cover for our swing set. Take measurements of the frame that the cover would have to go on. Then do a search for replacement swing set covers. Once you find some manufacturers, take some photos, and call them with the dimensions and send the photos by email.
Your other option would be to contact the local sunsetter (or equal) shops, and see if they do custom work.
Finally, I think JoAnn's fabrics sells canopy material, you may be able to find someone on this site with the equipment to sew it.
Hope the helps.