Yeh, the 20 is finally out. A bunch of places have it. I think it is hurting sales of the 12. I saw the 12 for $299 the other day. Cheapest I've seen the 20 is $347.
I'm gonna wait till Black Friday and if somebody has the 20 at a great price, I'm gonna jump.
$380 at PSA with free shipping on the 20 GA.
http://palmettostatearmory.com/mossberg-590-shockwave-20ga-shotgun-50657.html