Dura Ace 7700 (with American Classic RD205 rear hub) Broke Shifter. Upgrade Options
If you want to keep with 9-speed and Dura Ace level, options are following:


New Old Stock. You can probably find and exact replacement on eBay or some shop that specializes on old parts.
Campagnolo shifters, either 10-speed with Hubbub cable routing or Shiftmate 2 or 11-speed are compatible with Shimano derailleur and 9-speed cassette.