Another possibility for supporting a concertina, especially when standing up is a neck strap (similar to those used by Saxophonists). I've seen concertinas with rings fitted to the ends for clipping on a neck strap and someone I know straps dog collars (not the clerical type) round the ends to clip on a neck strap for playing standing up. I have rings on my anglo straps for that purpose, though it was only meant to be a temporary measure until I could get around to fitting something more permanent. Round tuits have got expensive, though :-)