Caribbean, Latin American, and West Indian markets often have a more consistent stock of fully ripe (black) plantains.
If your store only has green plantains but you want sweet ones: Store them at . buy plantain
If you can't find ripe ones, many stores sell frozen, pre-sliced Goya Maduros in the frozen food aisle. Where to Buy Caribbean, Latin American, and West Indian markets often
Choose "big and chunky" plantains, which are often twice the size of a standard banana. many stores sell frozen
You can find fresh plantains at most major retailers and specialty markets: