The state of CA will reproduce the legal YOM plates for your car if it's 1962 or 1963 or earlier. No w113 chassis car will qualify for that. There are companies on the net that will produce a 2nd CA plate from a photograph of the 1st one. They usually do not ship to the state of CA directly. I believe these are not by the letter legal for use on the roads, unfortunately.
The 356 forum has a lot more information on this subject. I believe this is explained by the fact that the YOM plate laws of CA allow pre-A and 356A vehicles to take advantage legally, whereas later cars such as the 356C and the w113 SL cars can not.
BTW, I believe that if all YOM plates were obtainable, which they are not, the black/yellow plates would only be correct for 230 snd 250 SL. I think the style changed in 1968 to blue/yellow, but I could be somewhat wrong about the exact date. I have the black/yellow plate that came with this 230SL, it is currently well-preserved in a box of oily/grimy rags. If I sell the car, it should go with it.
Again, I am not completely sure about any of this information... it's probably all changed.
1967 230SL (Manual)