45000 miles. Thats pretty low miles for a smoking engine. Either the miles were popped (over the years Ive had several trucks that were pooped), air filter is not right(motor dusted), or the oil was never changed. My 2 cents Mitsubishi's are prone to smoke a little starting in the 70,000kms mark but not bad.
Type in Japanese mini truck parts and you can order from a multitude of suppliers. I would highly recommend you get several quotes because parts prices will very.