Kutter gave great advice, as usual.
Baker forends show up often on Ebay, and I've bought two at very reasonable cost because the seller had no idea what they were.
Another great source for flat spring stock is lawnmower or small engine recoil starter springs. I also watch at flea markets, etc. for old key wind clocks, alarm clocks, etc. Broken electricians fishtapes, handsaws, plumbers snakes, and even old tape measures are sources of good quality flat spring stock of different widths and thicknesses.
I save spring stock whenever I find it so I don't have to search when I need it. It helps immensely to have a piece close to the correct width and thickness when you need to fabricate a spring. Simple spark testing with a grinder is a good way to tell high carbon spring steel from some alloys that are harder to heat treat.
I don't know the carbon content of flat steel banding, or how well it would temper into a spring. It takes a set very easily as is. So I'd guess it is probably no higher than 1050 to 1060.
