I've made inletting scrapers out of better quality garage sale screwdrivers, bent at about an 80* angle, rough shaped on a belt sander, then heated to red, oil quenched, polished and drawn to a light-medium straw. I've made inletting chisels out of O-1, heat treated the same way. When drawing the temper, heat the shank with a propane torch and watch the color change creep into the cutting surfaces. When it's a little bit light, remove the torch and quench in water. Carefully done, you won't melt the handles on plastic screwdrivers!
As for inletting rasps, are you talking about a series of discs or a cold-chisel cut form with actual teeth? For a disc type tool, I would look at grade 8 washers, stacked with smaller diameter 1/8" to 3/16" thick spacers between them.