The Genetic Research Lab is the perfect location for farming gene modification items.
Simply tap the Activity Overview on the top right, and select Genetic Research Lab under the Get Stronger tab as illustrated below:

The Genetic Research Lab is filled with multiple Elite Monsters and the Boss BF Mutant.

Elite Monsters drop genetic modification items upon defeat.
BF Mutant drops advanced genetic modification items upon defeat.

Defeating the Boss for the first time each day grants First Kill of the Day Reward which is sent directly to your mailbox.