Hi Richard,
The Don Johnston Switch interface is no longer being made, they stopped making these quite a while ago now.
For people needing a good quality switch interface for gaming, the Xbox Adaptve Controlelr is the cheapest and most reliable one currently available.
There are other switch interfaces available, but the vast majority do not work well for gaming.
They are also usually very expensive and often allow for only 5-6 switches to be plugged in at once. The XBOX Adaptive Controller has closer to 15-16 switch ports.
if the Cross Hair could support this device, it would be very helpful.