Arrow Springs still advertises glass dydinium plates (4-1/4" X 5" and 6-1/2" x 6-1/2").
http://www.arrowsprings.com/html/eyewear.html
Just for comparison: 4-1/4" x 5" - $125 (glass), 6-1/2" x 6-1/2" - $200 (glass)
6" x 6" acrylic - $100
12" x 12" acrylic - $400
18" x 24" acrylic - $1200