Search for “light table menu acrylic flashing” - there are 20 listings now with the cheapest (shipping included) now looks to be $5.66. I usually get 5 or 10 at once and use them for quick little light signs.
The plastic it ships with is really 2 sheets of thin plastic you slip a menu card into if you were using it for its advertised purpose. I throw those away.
Quick & easy to use.