Get blank Ducky ISO PBT white set. Get waterslide decal paper for your laser or inkjet printer. Not only will you not have to hunt them down, you also get the advantage of using any font you like in any colors your printer can produce. The only hard part of the project is putting the decals on straight, but you can make that easy if you print lines under the legend and use that as a guide to line up underneath the keycap edge so you can trim it off with a hobby knife.
Alternately dry transfer letters could be another easy way to go to accomplish putting legends on keycaps in harder to find layout choices.
