The best tool for the OP's type of fixed cup is the Hozan C-352 @
3alarmer mentioned above, or the VAR-30 or Campagnolo-793 others have mentioned.
The advantage the VAR-30 has over others is that other jaws are available to fit different styles of fixed cup. The Campagnolo-793 has flats on the body that can be clamped in a bench vise for extra leverage. All are relatively expensive compared to the home-made Sheldon Brown tool. Perhaps a local bike shop has the proper tool?