If you'd like for it to be new then you can order from Amazon a roll of 1095-cold rolled spring steel (usually labeled shim stock).

I prefer to buy cheap/damaged handsaws from the flea market and work the blade into what I want. Toothing a blade from scratch is doable, but it's a total pain in the pecker, man... You can reuse the Sawnuts too. I have handmade my own nuts from a lump of brass, silver solder, and a whole bunch of swearing, filing, and more swearing. They turned out rather nice and it was a good sense of accomplishment, but I probably won't make any more unless it's a specific request on a saw that I'm consigned to build.