Does anyone know where to find a DeVere yellow dichroic filter that will fit in the Ilford head? I imagine other yellow filters would work as well, but I would like to find one that gives the widest contrast range.

Background: I recently purchased an RH Designs Analyser 500 to replace the stock controller on my Ilford 500 Head. While coresponding with the designer on calibrating the system he mentioned replacing the green filter with a Devere yellow filter because it gives a better contrast range at soft grades. I would like to try this, but I am not sure where to find a DeVere yellow dichroic filter.