RealOEM is your friend. You can put in the 7 characters of your VIN and get the parts blow and numbers for you car. Also check with our sponsors. All of them are quite helpful and most offer OEM parts at less than MSRP.
Try ECS Tuning. http://www.ecstuning.com/Mini-2007-Cooper-R56-S-Coupe-L4_1.6L_N14B16A/Search/SiteSearch/Thermostat/
Thanks for the start, I'll be using RealOEM quite a bite till I get this running the way it should. ECS Tuning has very competitive pricing. Always looking for a better price. The sponsors are right there too.