There are two models I know of that will hold two 5g cornies and one 3g corny. Unfortunately, both are now discontinued by their manufacturers - but they were very common and still show on Craigslist (at least in my neck of the woods) with some regularity.
Sears Kenmore Elite 4.9 and Sanyo 4912 are the models. With minor modification of removing the shelving from the door both units will hold two 5g cornies, then you can rest a 3g corny on the compressor hump and prop it up in the front with piece wood.
I ran this set up for years (nice 3 tap tower on top, and hole through the side). I actually just upgraded to a 6 keg keezer, needed more on tap. Too bad you're not on the west coast, I've got this set up in garage just waiting for a new home