My ignition tumbler on my 230sl was split in half and it made it impossible to turn the key. After removing it from the column steering (see elsewhere on this forum for procedure...I'm warning you, it's a real job!) I discovered that it was impossible to find a replacement, Apparently, the tumbler for the 250 and 280 sl's is different than the one on the 230sl.
I found a fabulous solution on ebay. They remanufacture tumblers. Besides a new tumbler, you get 3 Neiman keys, a new chrome cover, two screws to replace the pins you had to drill out and an extra locking ring should you ever need to go inside. All this for 125$. Much cheaper than the alternative which was to replace the whole thing with the steering lock. You can find it here:
http://stores.ebay.com/Gullwing-Automotive?_trksid=p2047675.l2563 I'm in no way affiliated to these guys. Just wanted to convey the info, should it be useful to anyone.