When will the train schedule be available for trips from Florence to Rome FCO in October, 2023?

Hi October is part of the summer timetable. Generally would expect to see these from June onwards. 
so set your self an alert and just keep vigilant particularly if there is a specific train example high speed . Note sometimes the fast trains might get loaded after slower trains.
Goodluck ! It will work. 

The schedule generally time wise does not change and tickets will be available a month ahead