@beaucarnes I am not sure if there will ever be an official UART cable, especially since you must be very careful wiring this up. You only want to use three of the four pins in the UART connector when connecting it to a Raspberry Pi. This is because one of the pins supplies 5VDC power, which is not used for serial communications, especially since the RVR’s and RPI’s UART pins are only rated for 3.3VDC.
Here is the Getting Started Guid from Sphero for how to wire the RPi to the RVR.
The jumper wires that most will use for this purpose are readily available. For example…
You just need to ‘peel off’ a group of three wires from the bundle, and then wire the two devices together as shown in the Sphero Getting Started guide.
Hope this helps!