I'm looking for the Optional USB2 interface for the U-trak trackball. I have looked on Ultimarc's website but I cannot find just the USB interface, they only give you the option to add it when you purchase the trackball. Does anyone know if they sell just the Optional USB2 interface or where I can find one. I have looked all over and can't find any info. I also tried to contact Ultimarc but haven't received a response yet.