I really have never saw a starter kit for a flintlock. All you would need to purchase is a 3gr pan charger flask,wooden ball starter, clear see through powder measure, some patches, bore butter, roundball, a few extra flints (Thomas Fuller Black English 5/8-3/4 should do.. I like the 3/4), then at the hardware store get a small hair paint brush (that will clean out the pan better then any of them they want to see you), aome isopropyl alcohol, car windshield washer fluid, and you can make your own knapping tools.

In an old plastic ketchup bottle, can clean them out and make a powder horn. Just be sure all the moisture is out of the bottle before you fill it. Since he is using a flinter only Black Powder will do of course. Get the 3f grade as that can be used as the main charge and as the pan prime. In another bottle mix the alchohol and car windshield washer fluid as a cleaner. And he should be shooting in no time.