Where to find plastic like in film conversion boxes?

Where would you go to get thin, grainless semi-opaque semi-translucent plastic like that found in film-to-video conversion units? Ideally, hoping
to find a place in the Orlando FL area that might have it. The grain of the sheet needs to be non-apparent when light is projected through it and thin enough that it doesn't perceptibly blur the image. Also can't be glossy or the reflection of the capturing camera will be visible in the image.
Thanks for all input.
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Autymn D. C. wrote:

That must be drafting Mylar. It's intended for light passing through in a blueprint machine.
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