Such controllers are available from several sources. The system would include the acid tank,perstaltic pump to dispense the acid, the pH controller electrode, and the associated control electronics. This equipment is not cheap by any means and will require regular maintenance to keep it running properly. IMHO, it will take you less time to test your pH once a week and add acid as needed. These types of automated systems have been used in commercial pools for many years but remember, they have trained staff who maintain this equipment, sometimes on a daily basis!
In my previous house I used a peristaltic pump with a 5 gal plastic drum and diluted the acid 4 to 1.
The pump had a run time adjustment on it. I wired to come on with the filter pump. It took some time
to get the adjustment correct, but it seemed to work well when I remembered to fill the drum.