Buds sells them.
There is also a Weatherby version. It has screw in chokes and costs about $100 more.
They are basically the same gun. Reviews are positive on both, but the Weatherby is said to be finished a little nicer. I have seen the Mossberg advertised for about $425, and the Weatherby for $550. I like the idea of the screw in chokes, but for my purposes, it really isn't an issue.
I have been considering adding a 20ga semi to my collection...one of these two, or maybe a used Remington 1100. Still investigating