For the interested,
alibaba.com is something like the amazon equivalent for manufacturing suppliers. A lot of the sellers only deal in large orders (a couple I saw had minimum orders of 3 40-foot containers [!] as their baseline). I found one supplier with a minimum of 50 packets for B4-size paper, however, with the option to negotiate.
As a general (OT) tip: alibaba is *amazing* for ordering in bulk direct from manufacturers. If you ever want to buy a few thousand of something custom made, they're your new best friend.