You have a couple of choices, that's for sure. One of the best is to look on that online shopping site and buy some old molding planes and modify the plane irons and even the bodies for your use. You can remove stock or glue on stock to the bodies, and the irons can always be made smaller or re-shaped in profile. Another possibility is to make your own using flat spring steel stock. This is available at Brownells or other places. Most small molding planes have thick irons but if you are willing to go thinner, you could use the steel from antique one-man or two-man crosscut saws. The most difficult and challenging option is to use OCTS steel. That's a joke among blacksmiths. OCTS means "Old Chevy Truck Springs". These can be used to make almost anything a blackpowder guy could want that is steel, if you have a way to cut and shape them.