Build yer own...

Supplies:6 business cards per box unit, and a hacksaw (just kidding).

Align 2 business cards in a "+" shape, as evenly as possible.

Bring the bottom two flaps up over the top card...

and similarly fold the side flaps over the top.

Create 3 such units of 2 cards each (for a total of six cards), then disassemble all of them. Take three of the newly folded cards and arrange them as shown.

Now add the other three. There's no good way to explain this except that the flaps should hold all the cards together. It will be surprisingly sturdy and you can connect multiple boxes together without adhesive of any kind.

If all else fails and you become frustrated beyond reconciliation, feel free to send me your extra business cards. I'm going to need at least 7,000 before my project is done.