You could likely swap the tranny from the CL6speed. Finding one in the junkyard should be nearly impossiable for you so the dealer will likely be the only option.

A cheaper alternative but not buy much would be to install the 5speed auto from a standard TL/CL into your car if you want to shift gears. Just make sure it's had the warranty issues fixed first. You should be able to find one remanufactored with ease.