Luke is the #1 go-to as mentioned above for anything 4104 specific, while most of the engine parts and many other pieces can be commonly sourced from other suppliers as well. Sometimes you'll have to get a little creative as some parts may not be available directly but there are modern components which can take their place (and often act as a direct upgrade in some ways), while certain parts - especially if you're looking for marker glass or rear windshields, that sort of thing - you just need to scrounge classifieds and eBay.
When in doubt - ask here!
