My first instinct is to advise the OP to give this job to someone who understands what grade of steel to use, and how to properly heat treat it.
A beginner determined to make a spring is probably better off buying a piece of annealed high carbon spring steel, and concentrating on correctly shaping it. Correct hardening and tempering will be another educational experience.
Anyone who plans on working on guns as a hobby would do well to latch onto every piece of spring steel they can save. I have a nice selection of new annealed spring steel and quite a variety of flat springs from various sources. Old clocks are a good source of thinner and narrower spring steel. A return spring from a broken tape measure was recently found to be a perfect thickness for a Lefever cocking indicator spring. Recoil starter springs from small engines are a bit thicker. Brush-holder springs from old DC motors are another source for thin stuff. Hand saw blades, as mentioned, are usually high carbon steel, but a lot of the thicker powered hacksaw blades are alloys that can be more difficult to heat treat. The flat springs from animal traps are another common source. The springs from scrap cable retrievers supply a lot of quality material too. Automotive leaf springs used to be mainly carbon steel, but newer cars and trucks utilize a lot of different alloys.
The trick to using all of this readily available supply of free or very reasonably priced spring stock is properly annealing it without excessive scale formation. When a furnace is not available, you can do a good job by putting your pieces of hardened spring stock in a short length of threaded and capped black pipe with a small vent hole. Put some brown paper bag inside to consume the oxygen when it ignites, and bury it in a pile of hot coals from a large wood fire. After 18 to 24 hours, the coals slowly die out and cool naturally. Long heating to a dull red color, in an oxygen free atmosphere, with very gradual cooling, is the key to annealing. The steel will be dead soft, and virtually free of scale.
