DIY magnetic cards?

[wojtek]

I have no experience and even have no card reader, but you coud start with a piece of VHS tape (computer megnetic tape would be better but is not easy to get). Then line it with a piece of thin and stiff paper and cut to proper dimensions using paper cutter.
VHS tape width is 12.7mm or 1/2", the card dimensions are 11.3 x 71 x 0.2 mm (not sure about it, found somewhere in the internet).
Anyway you could give it a try.