I lived in Costa Rica near San Jose for eight months a few years back. Work took up most of my time, so I only managed to get out on a charter once. The ocean fishing is great.
The Tico Times is the English language newspaper, and they have a weekly fishing column. Here's a link:
http://www.ticotimes.net/fishing.htm
There's a hotel in downtown San Jose that is "headquarters" for the traveling fishermen. Many stay there, and there's a booking service for all kinds of guides and resorts. I don't recall it's name, but anyone in the area familiar with the fishing scene would be able to hook you up. (Hint: the building is pink stucco, and the bar is infested with pretty girls.

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Have fun down there. Costa Rica and the Ticos are great!
Mike