The easiest way to deal with this, is take one of your existing feet to a hardware store and use their screw guides to figure out what size screw you have. Then you can probably rig together 4 new feet using random stuff at the hardware store. Just make sure that the bolt that you purchase isn't too long because if it is, you may accidentally rip out the screw insert.
At the very least, you'll know the correct kind of screw foot you need even if you don't use hardware store parts to put one together.