There's a whole game for sale in Mechanicsville, VA with a perfect BG according to the CL ad. If you just need a better one, buy the game, swap BG's and sell the game.

Back in the day original NOS BGs were selling high dollar...I think Steve Young at PBR did one run of repro's, so you might contact him to see the chances of doing another.

You might also try Ron and Nancy Webb: http://pinballglass.homestead.com/ They are licensed Gottlieb and there was talk at one time of them repro'ing the glass too.