RE: Standard size 400 brushless
Eflite Park 400, Himaxx 2025 series are what I can come up with off the top of my head, but be careful. Many "Speed 400" gearboxes aren't designed to handle 200 Watts, the kind of power a brushless "400" class motor is capable of.
You can also get pinion gears bored for 3mm shafts.