There is a nice-looking 56 key Lachenal Edeophone coming up for auction in Birmingham on 17th July by Auctioneers Biddle and Webb. It doesn't say whether it is extended upwards or downwards but looking at an end view and the button layout, I think it is most likely to be an extended treble. Correct me if I am wrong. This is the description from the catalogue:
A Lachenal & Co 'The Edeophone' concertina, with black ebonized body with fretwork end sections with 56 buttons total, registration number 129662 and numbered 59351, housed in a later fitted case. Estimate: 500 GBP - 700 GBP - A bargain at that price! £2500+ would be more like today's current value.
Here is the link: http://www.the-saleroom.com/en-gb/auction-catalogues/biddle-and-webb/catalogue-id-srbid10048/lot-e921e108-5f2e-437b-8725-a4cd00f01ef4
Chris