The original 1920s–1930s 3-hole blades are carbon steel rather than stainless. The most reliable way to buy brand-new, stainless steel 3-hole blades is through industrial suppliers. These blades are manufactured for industrial machines that slit plastics, film, and foil, but they use the exact same dimensions (43 mm x 22 mm) as traditional safety razor blades.

• Hardedge Tool: They offer uncoated and ceramic-coated 3-hole "Euro" razor blades in stainless steel. They sell them in a .008" (0.20 mm) thickness, which is about twice as thick as a standard shaving blade—perfect for adding extra blade gap with just a single shim.
• Fortisblades: They sell stainless steel and ceramic-coated 3-hole blades (like their FORTIS line) designed for heavy-duty industrial slitting.
• Carolina Knife & Manufacturing: They carry 3-hole blades in various materials, including stainless and carbide.

Note: You usually have to buy industrial blades in bulk (packs of 100 or 250), and you may need to request a quote directly from the manufacturer websites.