I am trying to find a 12v input and 12v output breadboard power supply but I can't find one. I am making an arduino-controlled lock but the Arduino cannot power the lock strike by itself so I need to use a seperate power supply. The link to make things clearer: http://www.instructables.com/id/Arduino-RFID-Door-Lock/#step0
There is nothing special about a "breadboard power adapter" that isn't served by a normal regulated supply. Simply use wires or a barrel jack or some other connector to connect any regulated supply to the breadboard as desired.
They sell 5V/3.3V breadboard supplies on eBay for $3-$5 shipped from China. Buy one and rewire/modify it to bypass the voltage regulator