We use standard LP boxes that are used by the industry to send us new releases. They hold 1-3 discs We have hundreds of these from over the years.
As suggested bags has them. Try U-Line.com - my guess is cheaper, box # S-167 The standard Weyerhaeuser box is RM50-203
We place each LP in a plastic sleeve, and use 2 sheets of flat 12" sq cardboard, inside the box, in front and back of the LP.
B The ARChive of Contemporary Music