Unlicensed cards can literally come from anywhere/anyone. Some of the most common were card show sponsors. They'd produce a set of cards to hand out (or sell) at shows. Local card shops would also produce their own cards to sell at their shops. Larry Fritsch being the most famous. With the advent of cheap technology, the internet, and ebay; now every Tom, Dick, and Harry can produce cards and sell them across the globe.
In my humble opinion, unlicensed cards pollute the hobby.
Someday my cards may double in value and then be worth half of what I paid for them.