I have been looking for a specific engine for my car. I am looking to buy a chevy small-block V6/V8 with Active Fuel Management (http://http://en.wikipedia.org/wiki/Active_fuel_management) which is where you can turn off one bank of cylinders to increace fuel mileage. I cannot find any engines like this for sale, I dont care if it is a crate engine or comes already built.

Welcome to AF, at this point I do not believe any manufacturer is selling crate engines as you describe. A salvage yard would be your best bet but you will need the harnesses and pcm also.

I have been looking for a specific engine for my car. I am looking to buy a chevy small-block V6/V8 with Active Fuel Management (http://http://en.wikipedia.org/wiki/Active_fuel_management) which is where you can turn off one bank of cylinders to increace fuel mileage. I cannot find any engines like this for sale, I dont care if it is a crate engine or comes already built.
Your link does not work, but we know what you are talking about.

This technology has never been applied to a traditional-design small block Chevy that I know of.
I recall this kind of system not only cuts off fuel to inactive cylinders (that's the easy part) but also leaves the corresponding exhaust valve open at certain intervals. Such a system would require extensive modification of the SBC valve gear, which, as far as I know, has not been done to a SBC by anyone.

There are other (non SBC) V8's that do use this system; as noted above, the wrecking yards is the place to source them.

Frankly, the only reason to use active fuel management is to save fuel. There are many ways to build a decent, fuel efficient SBC without resorting to such systems.