Well, you called me out here on something off topic, so I'll reply here.actually, we have just one. don't confuse the cat for the resonators
Better get to know your V6 Accord better...
Look at your exhaust manifold (both of them) and you'll find the 2 "primary" CATs. They are very close to the engine so they heat up as fast as possible.
Then follow the pipe and you'll find the one under the car, and that would be #3.