If you've recently bought a set of K-Planes then they most probably came with the electronic sensors on them. And if you are using mechanical indicators, there is no reason to use them.

I'm looking for a new set from such a purchase.

Found one on the forum but was a day too late.

Must be more out there!

Certainly someone on this forum must have bought a new set of 280S or 380S with these sensors and is hooking them up with mechanical indicators