Does anyone know/have a big brake kit for the countryman?

 

I'd look into the 135i as an OEM BBK.

 

How do you just look into it?! Test fit it?

 

basically yes, test fit.
Check the rotor 'hat' offset to start. If not the 135i, the 1M would be an even better bet.

Most of the time in OEM BBK's the rotors & calipers will work, but you may need custom carriers or a basic shim. I know on VW swaps, a 2mm washer on the carrier makes everything align perfect. direct swap