I don't have a "Source", BUT you might try this: I had a Tucker 443 that had Fixed, non openable windows in the doors. They were plexiglass which was old and scratched up. I took the machine to an automobile glass shop who replaced all the cheesy plexiglass with Real automotive safety glass and at their suggestion, they converted the front windows in the doors to 2 piece sliders. They quoted me a 350$ price to replace all the glass less the windshield, about 7 pieces. When I went to pick up the machine they still only charged me the quoted price even though I was expecting to pay more. It was a bunch of 'Old Timer's' and it was several years ago so I doubt if you'll find quite that good of a deal. Later I went and priced pre-made aluminum sliders from various RV Trailer places and found that they were way too expensive. You might find a pre-made one (or Pair) thru a catalog sales outfit for a more reasonable price.