Where is the GFCI ?

[a/v nut]

I'm helping a friend extend a stand-alone commercial building outdoor outlet with rigid conduit and tripped the circuit/outlet by shorting it prior to working the box. Very small spark for 20A so I assume that the circuit is GFCI protected (as it should be). This is an old building and I can't find the standard GFCI outlet or dead front to get the power back on. I also took a quick look at the breakers and noticed some different colored ones (green, red, white) but no luck after flipping off and on. Any Ideas on where to look or what to look for?

[Fischer]

Is anything else or any other receptacles non-functioning? That might give you a trap line to check. If you're extending another exterior GFCI take a sight line to the closest part of the building and then check the interior for a j-box.