Hmm,every site seems to have it,mercedesshop also
http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?header=header.jsp&footer=&product=0005010015&partner=mercedesshop&baseurl=http://catalog.peachparts.com/&clientid=mercedesshop&cookieid=1HK0PZTKO1HK0Q03KV
AFAIK these caps fit every MB PC model from at least the 50-ies through the light duty trucks to modern cars.OEM caps are Behr`s ,maybe Behr don`t make them anymore...Here`s the address of Reutter:

http://www.reutter-gmbh.de/
I made a serch ,seems like MB changed the caps for many older cars,i don`t know why,hmm,maybe if I ask a cap for my my w110,they`ll say "upgraded to 120 cap". And what you`ll get will be Behr.
http://www.peachparts.com/shopforum/showthread.php?t=110335&highlight=radiator+cap
http://www.peachparts.com/shopforum/showthread.php?t=104300&highlight=1.2+bar
http://www.peachparts.com/shopforum/showthread.php?t=80299&highlight=1.2+bar
http://www.peachparts.com/shopforum/showthread.php?t=30289&highlight=1.2+bar
http://www.peachparts.com/shopforum/showthread.php?t=60305&highlight=1.2+bar
Mystery..Anyway,I`ll stick to the original 100.