How did I find them?
I did a niche keyword search in Google Image search. Even some of the more general searches, like makita parts, show some competitors that don't normally hit the SERPs.
While I was doing some research in this manner recently, I saw some familiar names on the tool side that seem to be trying to take our idea and slowly work it into their site. But I know they're there, so I can monitor what's going on.