Over-ripe bananas are perfect for banana bread, but getting them just at the right stage when you want to make the banana bread can be, lets just say problematic. It seems whenever I go to the store to buy bananas, they are always greeen.
Over-ripe bananas can be saved for banana bread by peeling them, placing them in a ziploc bag and freezing them. They may go brownish, and when you defrost them they will basicaly liquify, but for banana bread this is fine.
If you like chunks of bananas in your banana bread, you can still use the frozen bananas, just mash carefully or not at all. I keep a bag in the freezer at all times and add to it whenever I have bananas too squishy to eat, when I have enough for a batch of b-bread, they are all there, perfectly ripe and waiting for me.