anyone know where i can get wheel locks for the W211 factory wheels?

preferrably an online source that is cheaper than the dealer.

Rock.

The dealer may be your best bet because most locks are Cone seat and Mercedes is rare using Round or Radius seat lug bolts. The Mercedes ones look very long comparded to others.

Tire Rack sells McGard Locks. Here is the McGard page showing the types available. Remember the W211 uses 14 x 1.5 thread size:

http://www.mcgard.com/automotive/pro...page=4&group=3