We do not. If you get a Mach 3 Head and wind up wanting to upgrade to the combo, we would suggest getting the BlockDock 12CB. This cabinet features the same 12" 250 watt Celestion CopperBack speaker that the Mach 3 combo has.
Do note: The BlockDock 12CB is not capable of mounting the Mach 3 Head, as the Mach 3 head is much larger in size than our Block Series heads. If you plan on running the Mach 3 with the 12CB (or any of our BlockDock cabinets), you will only be able to rest the head on top of the cabinet.