Hi Robby- just re-visited this tread and found your question...
I don't have a particular company in mind for the aftermarket- rad upgrade, however- - I believe that in the Hot Rods section, via search, folks make reference to upgrading the 500e radiator using an aftermarket company....
also, you may wish to do a flush engine cooling passages with the MB (powder'd/ acid?) when you do the rad replacement (for peace of mind and maintence)
good luck and hope this helps