Here are diagrams for some keyboard layouts I could make for you. 31 keys (with drone) are standard but you can have up to 38 buttons on a G/D or up to 40 buttons on a C/G.
I have listed only G/G and G/D here but I could also make: B/F#, Bb/F, A/E, or Ab/Eb.
Historically there were many ideas of what the “extra” buttons on a 38 or 40 button concertina should be tuned to. The layouts I have included showing 38 and 40 key instruments are just some of the more common of those historic layouts. If you would like me to make anything different do get in touch and I can advise if it is possible. Great variation and customisation is possible when everything is made by hand.
CG wheatstone layout anglo 31 keys
CG Jeffries layout anglo 31 keys
GD jeffries layout anglo 31 keys
wolvertonconcertinas.com 