i have recovered my Timewindows a couple times, just go to a fabric store, and get a double knit material that stretches nicely in both directions.
measure twice, have someone sew a seam to make a tube, and slip/roll em on, then remount the end plates, and good as new!
i'll get some pics of mine up later.
i bought them new in 88 or so, and they still sound amazing!!