The largest keepcase I have came with a TV series complete collection and is a beast that holds 36 discs on 12 spindles across its two pages plus the front & back surfaces. That does mean there are three discs stacked on each spindle and in an over/under arrangement, so it's not easy to access a particular disc if not on top, but at 2.5" wide is pretty compact for the count.
I've never seen its like for sale empty, but is marked as partnum 3603XXT so may be worth trying to contact Scanavo directly and see if they'd maybe sell you a few.