Chlorine is a gas at room temperature and pressure. It would have to be kept at -151 degrees F to be kept as a pure solid, which is generally not conducive to being thrown in to an 85 degree swimming pool and certainly won't dissolve slowly over the course of a week. To achieve that it needs bound to something and CYA is a good binder of chlorine.
All tabs you'll find in box stores are trichlor and have CYA in them. Some pool stores carry the more rare calcium-hypochlorite tab, but they can't be used in the same feeder as trichlor ever was, some have binders that leave a gooey mess, and you'll have to deal with calcium buildup in your water. There's no magic solution, if you want pure chlorine you have to produce it on-site with a saltwater chlorine generator. Second best option is liquid chlorine which only binds the chlorine using saltwater.