[thekevan]

Do you mean just the lens? There's one in each of those old school overhead transparency projectors. Those should be easy to find.

https://www.bhphotovideo.com/c/product/592006-REG/Dry_Lam_50...

[arianvanp]

No that's a lens.

A Frensel reflector doesn't led light through bit instead reflects the light. Basically the same idea as the parabolic dish, but as a flat sheet.