I bought mine at Dick’s Sporting Goods. The hole in the middle is a standard 2” diameter. It happens to fit most (but not all) of my faceplates so I just choose to use the faceplates that it does fit.
Another option provided by a user is to get an empty gallon paint can and fill it with sand. Then make a segmented ring that has the inside diameter that fits over your faceplate and epoxy it to the bottom of the can. I thought this was a pretty clever idea.
