They can be ordered from McMasters-Carr. Check the clearance depth with a toothpick to get a handle on the length needed, starting with your frame thickness, and checking each hole depth. We ordered nuts as well, so we could chase the threads if we needed to reduce their length. Put a nut on first before cutting. this particular application is very tolerant of spacing, but try to make the center hole an accurate size for the motor centering boss. If I remember correctly, It was a D drill, with minor deburring. test in some scrap first.
