There are two primary sources for vintage refrigerators: Craigslist and Yard Sales.
I located the fridge for this on on Craigslist for $35.
"Note: there was not a beer tap installed in the door when I got it."
Step 1: Remove the Interior and Exterior Non-essential Parts
Remove all trim, badges, shelves, brackets, and other removable pieces.
Label each piece and place in a gallon ZipLock back immediately upon removal.
Step 2: Install a 4" Bread Pan Spacer in the Door
Place the bread pan exactly behind where you want to add you tap to the front of the door.
Copy measurements to the interior and exterior panels of the door.
Lay the cake pan face down and trace the perimeter of the INSIDE perimeter of the pan onto the door face - NOT the exterior perimeter of the pan.
Cut out so that the pan can slide into the inner opening and the factory lip of the pan sit on top of the door face and cover the hole that was cut out. See pictures for clarification.
Step 3: Install Shank and Faucet
Drill a 3/4" hole through the outer and inner door panels to allow for the shank to go through.
Insert shank and attach tap.
(TIP: Order an stainless steel spacer for the tap to upgrade from black plastic)
Step 4: Install Tubing and CO2 Tank
Purchase approximately 4' of gas line and 4' feet of beverage line from your local homebrewer supplier and x4 cable clamps.
Purchase a 5lb CO2 tank and gauge cluster.
Purchase a D Type keg coupler.
Run the beverage line from the coupler to the door shank.
Run the gas line from the coupler to the CO2.
Place a standalone temp gauge to monitor the interior temp analog-style.
Step 5: Prep and Paint
Sand down all surfaces and then wipe down with MEK or Acetone.
Paint with a paint and primer in one multi surface paint.
If your surface is less than perfect use hammer tone paint to heavily reduce your prep time and improve the quality of the finish.
Use a wire wheel cup brush on any old pitted used-to-be chrome parts before painting.
Step 6: Hook in a Keg and Drink the Fruits of Your Labor
Hook in a Type D keg (Bud, Bud Lite, etc)
Open up the CO2 and prime the keg.
Run a glass to clear the lines of cleaner.
Fill a glass and... DRINK!