I bought my Warrantech warranty at MBS Motors in Duluth, GA. (See our Featured Shops Page). I doubt they can sell over the phone but, if you're up for a trip to Atlanta...
My advice would be for you to call several places in your area that service MB's and ask if they sell Warrantech warranties. You don't have to take the car to be serviced where you bought the warranty.
Bill Wood - Webmaster