5 ft roll Spring Steel for Kalimba Tines 5mm floppy
Industrial spring steel can be cut to size, the edges can be smoothed, and you've got kalimba tines! Price is for a 5 foot roll, enough to make a 15 note kalimba.
To learn more, see this article on making tines from spring steel.
This spring steel is 5 mm wide (0.20 inches) and 0.8 mm thick (0.032 inches) and is a dark blue color as it is unplated.
You may also be interested in Bart Hopkin's book Marking Lamellaphones.