My son lives in Denver and bought a 2006 jeep commander that now has a exhaust leak that he describes as under the front floor board.The local parts stores do not have the exhaust gaskets for his jeep?
I'm in Oklahoma so I can't look at the jeep but do the later model jeeps still use the donut gaskets?

No doughnut gasket just ball flange at manifold .You probably have a broken ex stud or two at the rear of the head .Common issue with these .

Just did a 2000 dakota right manifold, it had no broken bolts but the manifold was so rusted, it was eaten away and was clamping on a very narrow margin and the bolts were much fun to remove. I got away with shaving about
.050" off of manifold.

Is there a gasket between the heads and the manifolds on the late models?
How did you remove the bolts?

Are there bolts at the ball and flange that might need to be tightened?
My son said the exhaust leak quiets down after the jeep is warmed up.

There is a multi layer, mostly steel gasket maybe, and I chiseled the bolts around for removal where the sockets of any size wasn't gonna get it. The dakota manifold was easily accessible with inner fender removed. Don't know about jeep.

Ouch! I've had to do that before.

He lives in Denver, so get him out there in the cold! At night (maybe even day), start the engine stone cold and quickly start looking with a flashlight. He should see the exhaust condensation steaming from the leak, same place the sound is exiting. That should take him straight to the leak source.