Another idea would be a Titanium nitride coating, it's an extremely hard ceramic material, often used as a coating on titanium alloy, steel, carbide, and aluminum components like drill bits to improve the substrate's surface properties, the coat is extremely resilient to scratches. The coating is applied by the more common physical vapor deposition (PVD) or chemical vapor deposition (CVD). I'm looking for a coating company to do this, try googling "Toronto PVD coating" or something, one of my friends did this to their Ipod covers, which ended up looking like this:
