9V to Barrel Jack Adapter - PRT-09518 - SparkFun Electronics
DIY 9 Volt Battery Connector for Free : 6 Steps - Instructables
Amazon.com: 9 V Battery Clip Connector, I-Type 9 Volt Battery Clip, 9V Battery Buckle Connector Hard Buckle Plastic Housing and Black Red Wires Leads Iength 5.9 inches (I Type Hard Shell 8PCS) :