Anybody recommend a choke for a CZ/Huglu 720?

[southGAlefty]

Recently got a CZ 720 20 gauge and put a Trulock Precision Hunter in it (I live less than 15 minutes from Trulock's office). I'm shooting the Federal Heavy 7's in it and am getting acceptable numbers, stroked one yesterday morning in Georgia at 35 steps. The Trulock constriction is .581, would like to have something in the .570-.575 range to test but having a hard time finding a choke compatible with my gun. Any recommendations?