Wow! You have a #17 head that cracked? How did that happen? Was it overheated? Anyway...
Martin's Import Salvage claims to have one (800-569-9711, located in NC)... also Action Auto Wreckers in Massapequa (800-562-8811). Oh, and European Connection (800-395-8636, located in KY)... and Ollies Used Auto Parts (800-559-5865, located in MA). Make sure they include the cam bearing caps, these are not interchangeable between heads! Even better if they include the cam, prechambers, etc etc. There's a guy on the forum who wants to
buy a used cam, so if you get an extra, maybe he'll take it off your hands.
I'd definitely try to obtain a #17 or higher casting if possible (I assume you are familiar with the infamous 603 head crack problem, and the fact that #14 and #15 castings are the "weak" versions). Casting number is 603-016-xx-01, below the #2 injector area.
BTW, you can get a brand-new #22 head from Mercedes for about $1700. Photos of my 603 cylinder head replacement are at
this URL.