http://www.customtint.com/page2.html
But you have it in your shop already.
Just print out a red with a lens or transparency on clear media.
Start with a small square at around 20% hold it up to a glass and go from there.
35% transparency or lens not the same as 35% legal tint, but work from there.
Make sure you laminate it with peanut butter so you get a nice streak when they open and close the window and the dog will finally have an excuse for licking the window.
they make transparent vinyl that would give that effect
did you try the tintdude forum?