There are many options depending on what you need. What kind of spares do you need?
Several popular ones are: Centro Marino, Pesqueros, Abernathys. They are all more oriented toward the
power boat/sport
fishing market, but have many common things.
Importation duty for a YIT is inexpensive (2%), but not free. I agree that I would not normally use the postal service, but there are many services for
shipping into Panama which make it convenient. I live in Panama now and ship things in quite often...no problem.
Cost of shipping varies mostly by
delivery speed. How quick do you need
parts?