So there's no power at the outlet right below the breaker box outside the house? Can you get access through an attic above the garage to see which wire set is running down to the outlet? Why are you testing all the breakers, did they not label which breaker powers that outlet? Do you see little green men running out of the breaker box? I've heard those leprechauns can be pretty awful, though not as bad as the gremlins.
Alternatively, I've seen where people have driven a nail through a power cable and caused it to trip and then it went bad so it never came back on again. Check the breaker that powers those outlets and switch the wire to another breaker and see if it works then? Is there a sub panel somewhere that could be powering the outdoor sockets (crazy but I've seen worse).