Hola there! There is a Farmers Market in Panama City downtown, it is called "San Felipe Neri" and is located on Ave Balboa right next to the "Mercado del Marisco" or seafood market.
I invite you to visit my blog and check out the photos and other info. on this subject: http://panamagourmet.blogs.com/cookingdiva/2007/04/for_the_love_of.html
Happy New Year!
Melissa