After exhausting all the local dealers who only bother to look in their current Parts Unlimited and Tucker Rocky books, I gave up on the locals and turned to the net. I found replacement lenses at Chaparral Motorsports. Very good prices and I'll let you know how fast the shipping is.
I actually had one parts counter flunkee tell me that "goggles are so cheap now, most people throw the old ones away and just buy new ones" I don't know about them, but my goggles cost about $45. That's not disposable in my book. I can buy quite a few $10 replacement lenses before the foam is worn out.