This mod allows you to convert 100% of production in a city to espionage like you can with research and culture. This mod has only been tested in BTS 3.13, though I don't see why it wouldn't work in an earlier version of BTS.
-Unzip the contents of this zip file to My Games\Beyond the Sword
-Firaxis and 2K Games for Civilization IV: Beyond the Sword
-Modders are free to use and redistribute these files.
Check here for the forum thread.
Convert Production to Espionage 2016-10-05
Convert Production to Espionage