What kind of "locking" barrel connector is this?
It looks like the company in the next link sell these connectors:
http://www.cliffuk.co.uk/products/dcconnectors/

the specific datasheet:
http://www.cliffuk.co.uk/products/dcconnectors/DCPlugSocketLockable.pdf

You can check if they have an distributor in your country and get it from there.
Hope this helps you!

We were also searching for this because off a Motorola FX7500 RFID reader.
Have a nice day!
Dennis Tessels.