Bob,
It's not for sale, but I have a 16 ga. long forcing cone reamer. If you get to that point, you can arrange to borrow it. BTW, One of the best decisions I made was having Heym make a set of open choke 60cm (23" and change) barrels for my 16 ga o/u. I had them made for Bob Whites but use them for all small game. I wouldn't worry about choke tubes.
Mike