The mission_builder_barton_waterduck.zip file you have requested: Tools and Utilites / BW's Vice Mission Builder - 893.87kb is not available. Perhaps try browsing all files for the game Grand Theft Auto: Vice City and upload any files you want to share or are missing. This is the only information we could locate:
Here is a program that will allow you to edit the main.scm file that you can edit the mission data from GTA Vice City (this should work with GTA 3 and GTA San Andreas also, but this is uncertain). Please note that it is highly recommended that you back up any files, just in case either you mess up your game or you do not like this modification.