Post on the Cruiser Log Crewfinders web site first: http://www.cruiserlog.com/forums/forum.asp?FORUM_ID=4
Panama will have boats coming from the Atlantic into the Pacific - they trickle in, a few at a time, and they head out again. The advantage (though small, IMO), is that you can work as a line tender through the locks and the boats will have a small glimpse of how you work.
Golfito - it's been so long since I've been there that I'm not sure how many boats are there getting ready to head west. I hope somebody else will be able to answer that.
the west coast sailing rag, Latitude 38 is another place to look - lots of boats head to mexico in the Baja Ha Ha regatta/rally which get lots of writeup in Lat 38. They have a crew party before the regatta (some time in late October/November? - check mag.) - look into that, too. When we arrived in Tahiti in 1992 I would say the majority of boats arriving in French Polynesia left from Mexico. I would guess that's still the case. You will find very few Atlantic coast sailors crossing the Pacific. Better cruising grounds in the Atlantic and Caribbean than west coast US, I think.