I believe that the German built locomotives on IRCA were undoubtedly purchased because of the German money control laws during the 1930s. Hard money could not be transferred out of Germany. So foreign companies making sales into the German economy had to use the proceeds within Germany.
How I don't know if United Fruit had sold enough bananas in buy the locomotives. Maybe they did. Or maybe they made deals with other companies stuck in the same position to acquire their reichsmarks and thus fund the purchase.
BN