Phatman

I just purchased an M4 (American) and it only came with 1 choke tube (Modified). I shot some 3 inch turkey loads in it at 30 yards and was impressed with the pattern. My question is where can I buy more choke tubes that are standard tubes for the Benelli? Or maybe I should ask who manufactures the Benelli tubes? The tube I have seems to shoot just fine and I want to purchase more. No need to brake the bank with other tubes when Benelli's work just as I want them to.