I went to a couple of hardware stores (Lowes-like) and those guys had no idea what I was talking about. They kept trying to sell me a dovetail.

I think the problem is either the people at the crap mega hardware stores can't comprehend what I'm asking for or I don't know what to ask for. All the Mom & Pop I know of hardware stores shut down in the last three years so I'm left with Home Depot, Lowes and Harbor. Before I make the trip all the way out to Harbor, I need to know what to ask for.
Basically, I need a router bit that can be plunged and cuts this pattern: