Anyone know of an amplified handset for old Merlin phones?

There out there. Try Refurbed Suppiy or Mikr Sandman.

I had a Customer that need something like this on a Partner system.. Ended up trying a Clarity HA40 amplifier. They loved it and ordered another one. Pretty nice little unit and the price is right.

Ditto on the HA40's, we have used then also.

Mister Sandman, play that song for me. Please visit this link for some love.