Like davecharles said, there isn't just one answer.
* Older 1100 barrels are very thin, and there is not always enough metal to just bore/thread for chokes. These can sometimes be swaged out to allow for threading, but there are other issues that may prevent it (hard spots, out of round, off center, brazed ribs, barrel lugs, etc).
* Briley can thread for their thin choke tubes, but it will cost you the same or more than a new barrel.
* You could also have the shortened barrel backbored to give you a choke constriction, but finding a smith that can do it may be hard.
* Threaded 22" 1100 barrels are easy to find, and take easy-to-find choke tubes. Here's one