(Im a fairly new Mac user too so still working out where the app files are etc)
Go to /Library/Application Support/Bitcoin to find bitcoin's data. wallet.dat lives there.
To dump a private key, do thus:
1.) From Menu, click Help > Debug Window
2.) Click on Console
3.) type dumpprivkey [bitcoin address]
T.
Or you could import the private key you just dumped into Armory. I assume Armory has an import key command.
this still true for a mac say with 0.14.2 core
I could use a way to get one address's key's as I think i need them