Kitchen light lenses? Help!

Ok, so I have this custom light fixture in my kitchen, and the lens covers are all discolored and/or cracked. I have looked for this material or something like it at all the big home improvement stores, and I can't find it. Nobody that works there can understand what I'm talking about because I don't know what they are actually called! :surprise: I assume I would buy this stuff in sheets and cut it out? Can someone link me to, or tell me where I might find this stuff?! Thanks so much!