Asking the F/As nicely for *A* safety card (not *SOME* safety card*S*, mind you) almost always works. Just ask if they have an extra, and nine times out of ten, they'll walk to the seatback of the last seat in first class (or the first overhead bin in coach, wherever they keep the extras) and grab you one or two. It's not like you're asking them to let you have the second engine, because you read that a B737 can fly on one.
Writing the airlines honestly does not work. They get literally hundreds of requests a day, and simply can't honor all of them, so the vast majority now choose to honor none.