SL500,I can’t find the right alternator for my Mercedes-Benz. 2003 Mercedes SL500

I have spent the past week, and gone to at least 50 websites looking for the correct alternator for my Mercedes-Benz. All the alternators I've found are 12 volts 150 AMP. The original alternator i brought out of the engine, which i'm currently looking to change, is 14 volts and 150 AMP. This alternator came with the car. Please do you know a website where i can buy a 14 volt 150 AMP alternator that fits a 2003 Mercedes-Benz SL500? Please include direct link to the webpage. (if there's any.)
My car has an automatic transmission.