Visaton speakers... select the size for your loco, prices vary

292-530.. 2.5 inch square mount, large magnet full range speaker. Perfect for USA Trains locomotives

292-553... 2 inch x 3.5 inch full range 8 ohm shielded driver, low profile with a 4 watt MAX power handling

292-650.. 2" Full range Speaker Small locos like USA Trains S4