I spent 6 weeks in Panamá March to May. I took seeds and cuttings with me from ECHO. Declared all upon entry, was allowed to take all in. I would advise working with them to get a certification for what you bring. I did not have time.
I did not look for plants and seeds in Panamá City, but saw gardens in several places. I found plants, seeds, cuttings in Boquete, Panama. Some in farm stores, farmers markets, street vendors and from local gardeners.
On Isla Colon in Bocas Del Toro, I got most plants and cuttings from local gardeners who graciously shared what they had with me. Through talking with them, I met a plant seller in a corner of the town, Delihina. She operates out of a rental shop called Over the Water Adventures. Riding around on a bicycle It was easy to spot the gardens behind houses and stop to chat with the gardeners. Botanical garden there also source of info and plants, but I did not get to visit.
On Bastimentos island, Lo Loma Lodge has a master gardener, Mr. Kelly. Rich knowledge of growing everything!
Generous people everywhere!