My Lachenal 46 key McCann duet concertina is up for sale on Ebay.
It has bone buttons, metal ends and 6 fold bellows. I'm no expert but it seems to have steel reeds (i.e. they aren't the right colour for brass!). I bought it in 1994 and it had just been reconditioned by Hobgoblin (I can see new pads) and to be honest it has hardly been out of its box since.
All the notes sound OK and are at concert pitch.
The bellows are in good condition, and theres just a bit of scuffing to the leather on the ends (needs a bit of black shoe-polish). It has the original box, but the box lid has fallen to pieces at some stage and someone has handstitched a rather naff new lid and carry handle out of light tan leather (but it has kept the dust etc out OK)
Ebay link is here