Ok, this is his response:
Hi, Thanks, we’re out of the hand guards and have been for several months. I hope to have some more after the first of the year. The stocks are just a Benelli branded stock from another model of Benelli shotgun. SBE, or M1 maybe.
We’ll make it known if/when we get more on hand..
So I guess they were able to figure out that the stocks for another Benelli shotgun works also for the M4. I am going to do some more research and find out which one does, or if anyone might already know which one fits the M4 and let us know that would be great.