I don't know anyone hasn't mentioned it:
The easiest method by far to get maps of the world is to sack the portugese capital. Portugal is usually only has a strong navy, so if you can just get an army to their coreland they are pretty much helpless.
Other methods are trading map with Morrocco and then some west African nations. Also trade maps with nations all the way over the middle east until you get to Mallacca and the Japanese and Chinese CoT's which are rich but not very contested (As said earlier trading in Europe is rarely profitable).
The easiest method by far to get maps of the world is to sack the portugese capital. Portugal is usually only has a strong navy, so if you can just get an army to their coreland they are pretty much helpless.
Other methods are trading map with Morrocco and then some west African nations. Also trade maps with nations all the way over the middle east until you get to Mallacca and the Japanese and Chinese CoT's which are rich but not very contested (As said earlier trading in Europe is rarely profitable).