Cross Hex Tube: am-0756

[willzone1]

Hello,
I have a question about the "Cross Drive Tube, 500" in the kit of parts. These are the shafts/tubes that support the CIMple gearboxes. They seem quite important, yet I cannot figure out how to order more. We are using mecanum wheels, so we need 4 gearboxes, so we have ordered 2 more beyond what came in the kit. However, it does not seem that the gearboxes come with these tubes. They are not listed in the "Where To Get More" document, and the part number (am-0756) does not exist. Searching for the actual part name does not provide anything useful either.