I believe cube steak has been passed through some sort of machine, but I think Mindy is right - pulverizing it yourself may be the only way to get it.
aha, Wikipedia says this:
"Cube steak is a cut of beef, usually top round or top sirloin, tenderized by fierce pounding with a meat mallet, or use of an electric tenderizer. Many professional cooks insist that regular tenderizing mallets cause too much mashing to produce a proper cube steak, and insist on either using specialized cube steak machines, or manually applying a set of sharp pointed rods to pierce the meat in every direction. This is the most common cut of meat used for chicken fried steak."