SMF

I just discovered that those Feather single edge blades with the cutouts that fit some Valet razors are pretty easy to find on eBay. (I suppose some online vendors now carry them, too.) I'm pretty sure the ones with the blue and yellow triangles on the box (FAS-10 or "Seikan") are carbon steel, and the ones with red and black markings (FHS-10) are stainless. The stainless ones are about $1/blade, and the carbon steels are less.

If you use them in a Gem type razor, you'll need to transplant a spine from a standard single edge blade.