Are you asking for suggestions for interface boards (the components that actually create the servo PWM signals)?
Or are you asking for suggestions about connectors, wire, cable management, power management, etc?
What is the source of the servo positions? Arduino? Some other kind of microcontroller?
There are several Arduino interface boards that will handle multiple servo outputs.
Are these servos all together, or are they distributed across a large area?
Do you need a central source of 300 servo signals?
Or do you need 3 sources of 100 signals? Or 30 sources of 10 signals? Or 10 sources of 30 signals?
Does your application allow creation of a custom interface board to fit your particular configuration?
Or are you constrained to use off-the-shelf commercial interface boards?