PROJECT BOX 4.37" x 3.25" x 1.5" w/ 9V Battery Compartment, Gray | San Mateo Electronics, Inc.
9V battery holder with switch & 5.5mm/2.1mm plug : ID 67 : $3.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Project Box Plastic Case Enclosure with 9V Battery Compartment 104x64x28MM KE55 | eBay
HALJIA 10Pcs 9V Battery Holder Project Box with 2.1mm x 5.5mm DC Plug and On/Off Switch Case Cover Compatible with CCTV, DIY, Arduinos, motors, solenoids, LED strips: Amazon.co.uk: Electronics & Photo