On Mon, 25 Apr 2016 10:28:04 -0700, Don Y
wrote:

Generic credit card sized (business card sized?) PLAIN sheets of
plastic that are either very durable (unlikely to break when flexed)
*or* flexible.

Best guess I can come up with is a PVC gutter and a pair of shears?
(Hmmm... maybe a grade-school paper cutter might make easier
work of it?)

Damnedest things people can find with a 10 second search.

https://plastekcards.com/ (home)

_Blank Plastic Cards_ (PVC)

https://plastekcards.com/product-cards/blank-cards/