Jay,
I have some new, medium weight PolyFiber fabric left over. I can cut some off of the roll for you. I also have two (2) extra windows that I will NOT be using. These are just plain windws, and are from the factory. They would have to be sewn into the fabric I can send you.

(I ended up installing the factory sewn in windows.)

I would use the PolyFiber method of using MEK to remove the installed window and fabric, and then install the new one using the PolyTack cement to glue the new fabric to the existing. Iron the fabric only and shrink it at 300 degrees or less, and then use a brush to apply the PolyBrush, the PolySpray, and the Polytone color to match the existing.