Why can't I see the option I need under "Inverter Manufacturers"?

Options will only appear in this list if an inverter with that manufacturer has optimizer settings configured. This is done in the inverter editor in MissionControl, under “Required Optimizer”. For an inverter to be compatible with optimizers, either “Required” or “Optional” must be selected . 

NOTE: Inverter Manufacturer only lists manufacturers but will only be available for the specific inverter(s) under the manufacturer that you have set to allow optimizers.