If buying online, you'll probably have to settle for an unidentified "alloy" steel, but as long as they're not "stainless", they should work.
EDIT: Just to be clear, older DiMarzio models like the Super Distortion, Evolution, etc. use the 10-32 thread size. However, many of DiMarzio's newer designs use smaller 5-40 socket head screws that are a direct swap for the regular fillister screw type pole pieces. Both types of "hex" head screws look the same from the top, but the "set" screws found in the older designs maintain the same diameter down the entire length of the screw, whereas the 5-40 screws have a larger head, but a narrower shaft.
If you can find one in a chrome/nickel or gold finish that is not stainless, please post. All I can find are that are non stainless are black (which they already are.)