Hey we really are neighbors, I live in Costa Rica, right on the border with Panama' near Paso Canoas and about 10 minutes from Cañas Gordas.
I can totally relate to what you are saying as far as how stuff grows here. Btw, I am more or less an American expat. So I bet I can help you, and I am very happy to do so. I'm not allowed to leave because of child support laws. I pay every month but to leave I have to pay 13 months ahead, which right now I can't do. I've been here 8 years and speak Spanish like a local. I've been pretty seriously learning bonsai for almost 2 years, all on the internet. I am too far from San Jose to join the only clubs. I dont know how much you will find for bonsai there, and I'm sure where you are will matter. I mean for bonsai pots and supplies. I have found very little here as far as that goes, but two agriculture stores in San Vito ordered me a few ceramic pots and there are a couple plastic designs that are the "terra cotta" color. The selection is limited but I can get them for you at least, if you want or need to work it out. Also I can find decent bonsai soil now, but it took a while to find a source. But a nursery near the border reopened recently and they have several types of gravel that work and look nicer than the construction gravel I used before. I have no idea how much of that stuff you can find where you are. If you want to meet at the border I will be happy to get you what I can or take you to the places where I get stuff.
As far as bonsai stock goes, you can find some species of strangler figs growing in other trees and generally survive being collected. Ive gotten lucky and found some that are years old and come in a lot of cool shapes. Some can even go right into a bonsai pot or I use cheap plastic colanders to start training them down. You can probably find ficus benjamina in nurseries, tho some of the wild ones are better for bonsai. Generally speaking, any ficus you like will make an ok bonsai and they are tough as nails. Also you can probably get lots of kinds of bougainvillea that come in a lot of different colors, leaf sizes and flower shapes. Some are very cool for bonsai. I must have 20 different types for the yard as a natural fence and some on there way to being bonsai. I have several types of jades that some folks use as bonsai and are easy to care for.
I could go on and on with what I've learned about keeping trees in pots down here. So please pm me or ask here if you have questions or want to meet up. Like I said, I've been here long enough to help you with lots of things. It is my nature to help people when I can. So there you go, now you have an English and Spanish speaking friend that is into bonsai and not 1000's of miles away. I'm sure you are not more than a day away and maybe pretty close. My name is Eric, btw.
Welcome to the bnut and to Central America, a nutty place to live.
Oh, one important piece of advice- do your yamadory hunting during rainy season and it's best to collect or transplant during the full moon and the fallowing five days. I'm not joking, I learned it from the locals and it does matter.
Those look like manilla palms, aka arreca palms to me and they are common from here to Florida. There are cooler palms for bonsai down here but you may as well start with what you have..