I checked Dicks in my area and they did sell them but didnt have any in stock. You will probably find this problem everywhere since the 930SPX is a home run for Mossberg.
I got lucky and found mine at one of the shops that is a huge police supplier.
If you get one you wont regret it, from my personal experience. Mine runs flawlessly even with birdshot.
It seems to be very popular right now and as I was looking at pictures of the model listed below I noticed the pistol grip stock is identical to the one on my Beretta 1201FP that was made in the early nineties. Do the manufacturers buy the stocks from another supplier? The safety on the Mossberg is not very accessible with the pistol grip. Much better on the 1201FP. I like the way my 1201 feels and I'm sure the 930 feels similair with this stock.
Yeah, the stock is made by Choate and supplied to Mossberg. Mine didn't come with the pistol grip but I ordered one after getting my SPX. I haven't put it on as so far I am liking the way it shoots with regular stock. I have seen some pretty impressive videos of people running their guns with the PG stock though.