Don't know if you're aware of it, but the USA is getting the new C-class with a six-speed shift-it-yerself transmission. Only the C240 is available with the standard; the more powerful C320 comes only with the familiar five speed automatic.
I don't recall availability dates, but believe it is sometime this fall; check with your local dealer.
It's not much, but we at least have one Mercedes sedan available with the standard shift. If a new Mercedes fits within your budget, this may be a good option, as you'll be able to get warranty, service, parts, and such through normal channels.