Good choice mdntoilburner!!
Try looking on craigslist.com
A fellow w123 300D turbo driver parked next to me in a parking garage, and we struck up a conversation... he just bought his, which has 67K original miles in exceptional shape. I enthusiastically asked him how he found such a find.. his reply:
craigslist!
Autotrader.com is a good source, although there are sooo many cars on there that it can be rather hair-pulling to sort out the good sounding cars from the obviously shoddy mis-represented cars! Thats where I found my 84 300DT daily driver.. 1 owner, all records, low miles, and very very clean. Took me 6 or so months, but well well worth the wait!!
I was just in Ft. Lauderdale Fl., and took a visit to Mercedes Showroom (
www.mercedesshowroom.com) They had a very nice 300CD coupe, creme/palomino. Not sure if distance is a matter.
Good Luck!!!