Those small "hub caps" as on the 230SL first appeared on the 190SLs and 300SLs in 1955. In addition most of the ponton sedans of the era 180, 190, 219 sedans used the same hub caps. in the 60's as Sandcrab has indicated, many of the "finback sedans (180c, 190c, 200,220Sb, 230S, 300SE ) also some coupes and cabs, also used these hubcaps. Lastly they were used on some of the early W108 sedans like the 250S, SE, 300SE. That same small hub cap was used for decades on various diameter Mercedes wheels (13", 14" and 15" steel wheels). At some point some after-market supplier began supplying good stainless steel reproductions instead of chrome plated steel like the originals. I remember when those hub cap repros could be bought for $8.00 ea brand new. There are still lots of the small hub caps around used.
Now the solid chrome "beauty ring" is a different issue. The 190SLs had one, but theirs were for 13" diameters. Some of the sedans of the era used a 13" slotted chrome beauty ring. The 14" solid chrome beauty rings, like on your 230SL. could only be found on the early W108 cars like the 250S, SE or the 300 SE. So these 230SL style beauty rings are fairly scarce.