There was at least one production parametron-based
computer:
I have a Japanese parametron logic trainer. I think there are 12
parametrons in it, so it is not too useful.
I think parametrons died out fast because all other logic forms were
much easier to implement as speeds increased. Once the things get up
into the MHz region, tuning and phase shifting became real issues.
Nobody wants to tune logic - leave that to the radio guys.
--
Will