I checked also and say those.And I just checked Ebay and there are four Osborne 1's that have a keyboard with the solid arrow keys, so maybe these things are not that uncommon.
I'm not 100% sure but its a reasonable assumption.So you are saying the solid arrows are the mechanical keyboards. I need to go look at my computers.
Well with the early Osborne's ribbon cable pressing on the keys during storage causing the sticking problem on the membrane style boards, yes the newer style coiled cable style can still cause that if your not careful when you remount the keyboard to the case, I would think even some really low numbered Osborne's could have them as a replacement.OK, this chap here has the same keyboard with an OCC1 s/n 16448: https://munk.org/typecast/2016/02/16/paleocomputing-1981-osborne-1-cpm-portable-computer/
My OCC1 is in the 47xx range. So some fairly early OCC1s are around with this TEC keyboard.
I have not seen any vintage ads listing them for sale, so if Osborne used them or maybe they were only sold to to computer repair shops and not the general public I just do not know.When you say replacement, you meant by factory (either in or out of warranty)? I have seen no evidence that any 3rd parties sold these, but seem rather variations from factory.