Replacement taps for galley mixer units
On our 1980 Discus, there is a mixer tap in the galley, providing hot and cold water to the sink. Over the years, the inner spigot of the cold tap had split and worn down, until it had reached the point of no 're-turn'. We had been unable to operate the cold tap for the latter part of the season. Despite diligent searching, I could not find replacement tap handles anywhere.
The solution, in case it is of use to anyone else is this. I found, in a local DIY store, an 'Oracstar' kit like this  for installing a self-cutting mini tap into a 10mm copper pipe. The tap head has a small internal square section which matches the mixer tap valve perfectly. The kit cost approximately Â£5, which may be expensive for a tap handle, but it's certainly cheaper and less problematic than replacing the entire mixer unit!
An additional benefit is that the kit obviously provides you with a spare valve of the same size, in case it's ever needed.