My recommendation is to hit up a library or a book drive. If you’re looking for more wholesale needs, rather than retail, I’d hit up like an Ollie’s or Half Price Books. The latter will have some magazines, as well. You could always hit up some doctors’, dentists, or hospital lobbies for some magazines, too.
I am also thinking maybe someplace like bookoutlet.com or maybe thriftbooks.com. If all else fails, Amazon.