I modified a Frigidaire Model FRC445GB to fit a 1/2 barrel. It took some work but wasn't difficult. They sell the new version of this fridge at Loews. With some work you can probably use just about any 4.4 cu ft or larger fridge.
I'm the general manager for a restaurant and I am currently building a similar style into a bar that I acquired for free. I removed the angled lid and built a flat top. The only issue I have is the overhead clearance through the doors is tight. I have to lean the keg when putting it in or tap...
I layered three pieces of plywood (dug all the way down to coils) and it sits flush with the foam. I cut a 2.5" hole for air flow. Coils keep the tower very cold.