yes from the 1950's likely
the current similar model now has a more Italian style black keytop,
'which is more of a squared edge.
in order to find the same old type keytop, you would need a similar
old model Weltmeister that is only good for parts donation
it is remotely possible that Weltmeister
might have such old spare parts available
the black plastic keytop looks a bit like a little boat when you
see it upside down, fitting over the wood and glued into place
i would be more likely to think a woodcrafter in your area
might be persuaded to carve a piece of wood to fit, then carefully
glue it onto the wood still there after staining it black
if there is a junk piano handy you could start with a black key
and carve that one down to fit