The short explanation, in his own words:
I exported an Illustrator file with the numbers (outlines only, no fill) to .dwg format (readable by AutoCAD), scaled it up to the right size, and then sent the file to a laser-cutter (like printing).
There are plastic fabricators in Chicago like Petersen Brothers Plastics on Pulaski Rd. that can do it, usually they need a digital file that reads vector graphic information.
And these were the sad, little old ones:
Next up: Washing our home's filthy brick. Suggestions or services??