Look on North American Motoring, not cheap though.
Handheld Tuning comes to the N18 - North American Motoring
Drivetrain (Cooper S) - Handheld Tuning comes to the N18 - So we've been using the Stage X handheld to work with N14 and F56 Mini's as well as BMW F models for a while. What's nice is the client doesn't need to go anywhere or remove their ECU. They purchase the handheld, connect it to their car...