MB or Chrysler dealership. I found one in stock at my local MB dealership, they overnight/2day pretty much everything so if they don't have it you can get it quick. Plenty of threads with the part number in the technical section of the board.

As far as performance goes its going to suck more air in regardless of if you upgrade the intake or not but if you don't it will be very marginal. After doing both my readings from the ultra guage show a nice increase in the amount of air that is coming through. There does seem to be a slight performance hit in the low, low revs but that may be in my head. It definitely pulls harder up top though.