I have not heard of anyone reproducing these rear window's for the early Dart's.... but anything is possible. A used one may be the most reasonable to buy off this site, or any site really. I see your car is a 2dr sedan (post car) so finding one may be a little tougher. If no luck here, I would go to your local newsstand and purchase a Hemming's Motor News book, if you can find one, or go to their website
www.hemmings.com and you should be able to purchase a new one from a business or part's vendor. The only hold back.... is it could be very pricey to ship to your location! Good luck, and hope you find something soon! Dodge33