From the
article you mention:
it is like an Anglo in E flat and B flat, but with the push/pull reversed on both the right-hand end of the E-flat row and the left-hand end of the B-flat row. (In addition, there is a D on the pull on the right-hand row.)
So you can pretty much get there by swapping reeds around. I don't know if you can find an Eb/Bb 20-button concertina, but the same playing style should work in any key. On a 20-button concertina, swap the inside and outside reeds on the left hand row nearest the handle, and the inside and outside reeds on the right side row furthest from the handle. Some concertinas have differences on the far-left button on the left side, or the far-right button on the right side. You could get a few spare reeds to make the job 100% correct (although I wouldn't be surprised if those buttons varied in the "squash box" layout as well).
Here's Harry Scurfield's "squash box" layout represented as notes of the scale:
PUSH 1 5 1 3 5 | 7 2 4 6 6
PULL 5 7 2 4 6 | 1 3 5 7 3
PUSH 5 7 2 4 6 | 1 3 5 1 3
PULL 1 5 1 3 5 | 7 2 4 6 7
And a standard 20-button concertina:
PUSH 1 5 1 3 5 | 1 3 5 1 3
PULL 5 7 2 4 6 | 7 2 4 6 7
PUSH 3 5 1 3 5 | 1 3 5 1 3
PULL 2 7 2 4 6 | 7 2 4 6 7
