Yes, I should have included this in the article. I am overwhelmed with the immense support this has gotten over the last 2-3 days. These cards are generated one of three ways.

1. Generated incrementally from a valid number found on sites such as colnect.com

2. Generated using something called Luhn algorithm from a valid number.

3. Stolen from database leaks such as the Gyft hack https://krebsonsecurity.com/2015/12/password-thieves-target-e-giftcard-firm-gyft/