Can I get a male Thunderbolt to female USB 3.0 adapter?
The Thunderbolt port on your MacBook Pro is already faster than USB 3 so the fastest possible connection of an external storage device would be to attach a Thunderbolt drive via the Thunderbolt port.

Note that Thunderbolt is a faster interface than a hard disk can accept or push data so for top speed you will either need a RAID configured for speed or an SSD drive.