I can tell you one school (in Mississippi) that uses a formula to determine admission. William Carey University is a fully accredited private college that doesn't require a minimum GPA or GMAT score in order to get accepted into their MBA program. The formula they use is below:
(GPA x 200) + GMAT Score + (10 x Years of Managerial Experience)
Scores of 850-999 are accepted (with satisfactory application packet material) on probationary status. You must achieve a B or higher on the first six hours in order to gain regular admission status.
Scores of 1000+ are accepted (with satisfactory application packet material) on regular status.
This school use the trimester system, therefore, if you have a bachelors is a business related field, you can finish the program in one year.
There are a few online schools who do not set a minimum, but it's hard to find a reputable one. A great one that I've found is Florida Institute of Technology. It is a fully accredited brick-and-mortar college that have some fully online degree programs. Tuition is rather expensive ($2,000+ per class).