1" extension for 1.25" visual back

Hi,

I have a visual back that is only 1/6" in length that can accept
1.25" accessories before it hits a rear field flattener glass. I
need a 1" extension to make it longer so the diagonal inserted
won't hit the glass.

I only know of the Lumicon 1" extension of size 1.25". Anyone
knows of other brands that is 1" in size? Also are
their diagonals or adapters where the 1.25" is instead
screw into the visual back? (this is because my visual back
1.25" hole has screw threads inside).

Thanks.

Win