I had my R53 dynoed at Evolution Motorsports in Tempe back in the day, when I had the GIAC tune put on it, but we've not really had an organized "dyno day" anywhere since the Mynes guys moved to SoCal from Mesa.
Looking to get a baseline dyno to see where you stand now? They can vary a lot from brand and type of dyno, so if your wanting a baseline before doing some mods, you definitely want to go to the same place before and after to get the most consistent comparison.
Not sure what
www.evoms.com charges these days for a Dyno, but good/knowledgeable people there for sure, though not really MINI guys.