The C.O.R.E. inserts are completely different than a regular M&P. Do a Google search and you will see they changed their design.
S&W can barely keep stock of their regular M&P items - they don't make it a priority to sell retail...they ship most of their stocks to distributors. However, comma, like I said earlier - they haven't produced enough stock to provide to anyone.
Will keep looking. This is like trying to find a KT KSG or Sub2000 (Glock version)!!!