Wal-Mart, Home Depot and Lowe's sell Kohler replacement oil filters. As of June 2015, Wal-Mart sells a replacement oil filter for Kohler Command, Command Pro, Aegis, Courage and twin-cylinder Magnum engines that costs $10.97.
The Kohler oil filter that Home Depot sells is specifically designed for Kohler Courage engines and costs $13.21. The filter comes with a free ship-to-store option and a 90-day return policy.
Lowe's stocks a Kohler oil filter that is compatible with Kohler Command and Courage engines, and can be used with 18-, 24- and 25-horsepower lawn mowers. The filter costs $14.30 and also comes with a free in-store pick-up option.