It generally come sshipped in a cardboard box wrapped in plastic. WHen shipped in bulk it usually isnt cured so adding 50lbs of uncured rock into a tank will mean it will take awhile to cycle because of the amount of organics that are going to be broken down before the tank is ready.
I agree with NM Reef about hand picking each rock on your own from your lfs.
How much would it suck to order a box of 50lbs and end up getting a box with 2 25lb peices?