Try the cargo shipping co.s - Maersk, CSX, Matson and all the others along Maritime St, Ferry St and those along the estuary north of Jack London Sq. There is a very big post office on 7th St, near the West Oakland Bart Station and another in On Rydin Rd, off Central Ave., west of I-80 and I-580. Not sure if that is Richmond or El Cerrito.
I'm less familiar with the general freight lines but I know there are some on or near Hegenburger Rd toward the airport. Fed Ex is down that way.
Now 5 lashes with a wet noodle for making me remember that awful job I had at Sea-Land/Maersk. Actually S-L was great

, Maersk not so much.
But I'm retired to a big beautiful farm in the mountains and the boss who made my life so miserable, well they canned his butt not long after I quit.
Best of luck.