Before you buy from Ebay via China...Check Amazon...I have bought gears from this seller in the past and delivery is fast. He has or at least had many sizes and number of teeth too. There are also gears that need a 2.5 mm hole but I can't remember if they are for the axles or in the motor so its probably better for you to buy 'as needed' unless you are planning on buying huge Lots of broken engines.
Othmro US
Othmro US