I am sure there are many that have tried. There is a very expensive powder called lithium hypochlorite (about 5 times as expensive as bleach, chlorinating liquid and Cal-Hypo), but it is fast dissolving and apparently even under compression it does not bind well into pucks that would dissolve more slowly. Even Cal-Hypo in pucks tends to fall apart and has to have binders that don't dissolve readily in water so generally create a bit of a mess.
There is a product similar to bromine tablets called 1,3-Dichloro-5,5-dimethylhydantoin (DCDMH), but this is normally a powder and would leave DMH behind.
If it were easy to create a chlorine product that slowly dissolved and didn't add anything that would cause side effects, it would have been done by now. Chemistry just doesn't always give one everything one wants.