These bananas are on the northern half of Monkey Island.

How can I get there?

You're going to want to visit the cannibal village.

When you're in the rowboat, go to the north-most screen. (It looks like a duck's head.)

The village is in what looks like the duck's eye.

Some bananas should be near.

Have you walked to the leftmost side of the cannibal's village?

There's a bowl of fruit.

Take the bananas from the bowl of fruit.