I have a friend who just purchased a brand new Mac Mini. He has an older 20" Studio Display monitor and needs a cable to connect to the Mac Mini. Do you know where I can get such a cable?
You're looking to go from Thunderbolt/Mini Display to ADC (Apple Display Connector). ADC carries the power in the same cable so this might be a problem. Another thing, do you mean Apple Cinima Display? Because they never made a 20" LCD branded with the *Studio Display* name, no big deal (the 15" and 17" acrylic models from that era were called Studio Display). Check out this forum post;
Apparently, the solution is to go from Mini Display to DVI and then use another adapter to go from DVI to ADC. But this can only be accomplished if you have the external power supply for this display. Good luck.