Try this search: Mark Palmquist, Retro Radio Repair or this link: http://jmpalm.home.mindspring.com/
This guy vacuum forms replacement dial lenses. I've used him a couple of times, nice work and reasonable. I have also made my own with 2 part wood molds, .020 PETG and a heat gun, but for the price he charges your much better off ordering from him. Making your own can be time consuming. Good Luck!