A Duelist League can be found in "Toys R Us", "Books a Million", and other such places. Unlike a Hobby League, you don't need a UDE Number to enter, and you don't get monthly prizes. Although you may occasionally get a goodie bag, with a Promo Card and cheat booklet for a new Yu-Gi-Oh! Video Game.
The things that you can get from a Duelist League include:
Yu-Gi-Oh! Duelist League Pin Booklet Promo Card
In some stores for a limited time, they would offer you a common card just for participating.
The cards with set numbers DL1 through DL10 were issued by UDE until Konami started issuing their own, starting with the set DL09 (DL9 was used in the UDE series). The Konami sets each contain 20 cards that are available in "Colored" rare versions. So far, there are 9 sets: DL09, DL11, DL12, DL13, DL14, DL15, DL16, DL17 and DL18.