I need to find a router bit the will cut a "groove" with a 2.5 to 3
inch diameter. I only need the groove to be about 1/4" deep.

I saw one that was a panel cutter, with a 1.5 inch radius, but the
bottom was flat and the edges curved up. I'd like an arc, not a
"profile".

Anybody know where I can find this, or how I can achieve it with a
router?