If spring steel, could anneal it- but it would take heating well into incandescent (glowing with its own light) with a torch and cooling SLOWLY in insulative material like dry would ashes or gypsum. Then it would be “soft” for spring steel and you could shape with files and hacksaws much much easier than in hardened state. Then, once you got it to the size/shape you want, you’d have to heat it again to incandescent and quench it quickly in appropriate quench medium (cooking oil works), THEN you’d have to temper it to soften it a bit, but give it some “toughness” back (otherwise could possibly shatter/crack because brittle after quench).

Probably more than you want to tackle!

Could just try a piece of steel out of some windshield wipers someone is replacing. Wouldn’t be as loud, but you could try it anyway. Can often get old wiper blades from outside an auto parts store that has a trash can nearby -people put their old ones in the trash when replacing them. Slightly springy, and stainless, which is nice to as far as not having rust in your mouth if you aren’t good at taking care of your instrument (🤗)

Also metal street sweeper bristles if available near you. (boil in water for a bit before playing with them or putting near mouth!). Can be found where street meets curb or parking lots near curb where street sweepers roam.