First update. This is stuff I've already done, but the last post was long enough and it was getting late.
To tune reeds you need a tuning bench, and I've been making one for a while, when it's not been too cold in the garage. The plan was to only use material that I already had, which led to some heavier duty woodwork than first anticipated. The bellows is a PA bellows, new and unused. Slight tactical error in cutting the end frames down when removing them would have been better, but whatever.

Nearly finished when some bloke called Lester, from Wendover, revealed to the world his newly fitted air valve for his tuning table. Seemed a good idea, but I didn't want to nick one from a melodeon, didn't want to spend nearly £20 buying one, so I decided to make one.

Some piccies below. Buying would have been more sensible, but less fun. It's not very pretty, not very precise, but it works plenty well enough.

Frame, lever and spring. And hole. 

The pad - deliberately oversize, because the registration is a bit wobbly. It is faced with some felt and leather. Overkill, but good practice 

Pad glued on, with some cotton material and PVA. Not the neatest job. A small cylinder of white plastic completes the handle, but I forgot to photograph it. 

It works surprising well and holds pressure.

(I though I had some cupboard handles lying around, but couldn't find any, so the black handle in the pic came from B&Q for about £3. )

Well, useful facility for the mini-melodeon but not strictly relevant, you might think. No so. The mini-melodeon needs an air valve... and this one operates like a Hohner air valve.