The only places I can think that might have vice blocks in stock are Bradis/BradisII in Camby, or Elmore's in Greenwood...but I'd definitely call first.
You can also get them from Brownells or MidwayUSA, but you'll have to wait a few days for delivery.
Lay that upper on a carpeted floor and have someone stand on it. Put the armorer tool on the barrel nut and turn it by hand or position it so you can stand on the wrench and bounce on it.
Dont ask me how i know this!