Hmm, this is a proprietary woofer that is obviously no longer produced. Every once in a while you see parts for these on ebay. I do believe that you can use the studio series drivers as well, as an upgraded cabinet and crossover is the only difference between the lines. I am not familiar with what avguygeorge is referencing bhut that sounds promising as well.
Nice little speakers you have there...
-rob
Nice little speakers you have there...
-rob