I make all my own plug cutters for foam. I went to the hardware store and bought a length of 3/8" rod that I cut 4" sections from. Next find a piece of conduit that fits your needs aprox 6" long. Then take masking tape and wind it on the rod until it fits snug inside the conduit. Repeat this about an inch up the rod. Insert this into the conduit to just before the second wind of tape goes in and fill with epoxy, then push all the way in and let dry. Then with a dremel cut a section out of the conduit about an inch up for removing the cut plug. I also create teeth in the end of the conduit to help it cut better.
There cheap and work great, hardest part is finding the sections of conduit.