I've never heard of a choke tube "specially designed" for a Foster slug. You can shoot them out of rifled choke tubes. In my experience, including 2 different guns with two different rifled choke tubes, they didn't increase accuracy over a standard IC choke. One of my shotguns shoots best with a Trulock Skeet II tube in, the other with a factory Remington IC. You just have to try a bunch of different slugs and choke tubes. Best to get a good recoil pad first.