The last I heard, HR was out of the Tracker I barrels. I guess, if it were me, I would try to find a 20ga on the rack at a local store and Then send that in for a slug barrel. You could send off for stocks to get it the way you want it and that way, if your 30-30 barrel need bedding or any of that stuff you get you the accuracy you want, it wouldn't have to be messed with anymore. Its gonna cost you around $100 to have a barrel added at the factory, by the time you add the shipping and fitting cost. So, the difference in price isn't as much as you think, and you would have a complete 2nd gun and wouldn't have to worry about changin' forends back and forth. Just my 2 cents....food for thought.
cookiemann