I sent a mail with my post address to the local Hasbro office (in Germany) explaining my pool of nine players would like to join and asked them to send me a bunch of registration cards.Do you need to do this through a store? There's no gaming store where I live, so i am just wondering.
After the second reminder and several weeks they actually sent me two large blocks of registration cards.
If you only need a single DCI Membership number for yourself, just contact customer service and ask for one. This only took one day.