this place sez they have 'em
http://www.bagsunlimited.com/cart/browse.asp?subcat=587

this place says to store with tape reel vertical..
http://material-handling.globalspec.com/Industrial-Directory/open_reel_tape_recorder

when i was a kid, we had movie reels that were kept in an indexed
metal box, with a tab that would tip each cannister towrads you
perhaps some equip made for 6mm or 16mm movie reels would work for
your audio tapes?