Some of the garcinias we have in production are mangostan, parvifolia, forbesii, magnafolia, brasilensis, intermedia, madruno, prainiana. There’s probably more.
I recommend going to the Osa, but not really for looking for fruit. In that general region I would go to the San Isidro farmers market that is held on Thursdays. Two guys there specialize in rare fruits. Tonny Gracia has a large stand there and there’s an expat named Wade who sells some good stuff. Nearby is the farm of don Carlos. He produces some good durian and other rare fruits. You can find him on Facebook.
Two places in CR with very large roadside fruit stands are by the highway 27 in the vicinity of Orotina and also on the hwy 32 near the turnoff for Sarapiqui.
The farmers market in Puerto Viejo is on Saturdays.
Peter