You did not mention the year or chassis type, but like Larry, I have imported a number of W123 cars in the past and had to install A/C here, and then later I had the system installed by the dealer over there. They were Bosch kits for the W123 cars and had the same control schemes as the non-climate control units available as the factory installed system in markets outsie the US. I did learn that when you have them installed it is apparently a little extra work to properly connect the outside vents on the dash so they have heat and a/c coming from them, depending on the control position. The easy way only sends fresh or air conditioned air through them.
The last time I did this was 1985 and do not recall the vendor. He was in White Plains, New York though. There was ot trouble locating someone to do this then, and suppose it is the same now. Any local A/C specialists should be able to handle the job as the guys doing my cars were not making a living working on Mercedes-Benz cars, they handled anything with A/C. Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)