The current Drone Launching rules minimize the need for record keeping. However, if players don't mind keeping an individual datacard for each Drone-carrying unit or simply putting a fixed number of Drone counters next to each Drone-carrying unit, the table below can be used. Simply look up a unit's Rate and Reload threshold, and cross-reference the values to find the number of Drones the unit carries. Note this number on the unit's datacard and use it to keep track of how many Drones the unit has remaining.
Alternatively, simply make a bunch of generic "Capacity" counters, and give each Drone-carrying unit a number of Capacity counters equal to its Drone capacity. When a unit launches Drones, simply remove the required number of Capacity counters and replace them with an equal number of Drones. The only disadvantage of this method is that units with many Drones (like the Sakura, which carries eight) will end up moving around the table with a lot of counters.
Note: units that carry "Infinite" Drones don't really have an unlimited supply; it's just that they carry enough Drones that they're not very likely to run out during a battle.
Fixed Drone Capacity Table