Panama has a postal service, but they don't provide mail delivery to your home.American people mainly use U.S. based mail forwarding companies,if they live in some developed part of Panama.(costa rican border area/Panama city).
If you do live right in the countryside,as I do , mail is not an option,unless using DHl as they can keep mail and call me
to drive the 70 km to pick the stuff.
I will try to use DHL if I can find one in Borneo,but I guess the best way will be to bring the seeds back in my suitcase.
Unless I find someone in Costa rica willing to act as a receiver and in that case I could share seeds as well.But that
means quite an organisation