Perhaps somewhere, somehow, there is a Vauxhall that has the same throttle cable control unit but also has the radar sensors mounted in the front bumper linked to the cruise control.
That would have my attention. I would study it.
Nope, no such option available. *AND* even if it did, it would be far, far, far more than bolting on a new cruise, as technically the system is a lot more complex than something tugging on the accelerator cable.
At a minimum, you'd be reverse engineering the proprietary firmwares on the engine, TCM and ABS ECUs, and re-writing them to take into account the new functionality, and work out a way to communicate this across the ECUs in real time. You'd also as a minimum need the Stability Control version of the ABS system, incredibly rare in the UK.
Now on a 3.0l, there is no stability control option, and its not retrofittable to it. In addition, there isn't really a proper CAN implementation between the relevant ECUs, or capability to add one. Even on the later engines, the CAN isn't really a full implementation, so doubt you'd be able to get the required real time communication.
So, in summary, on a DBW Omega, if you had access to the proprietary source code for the ECUs, and the skills to program them, and assuming there was enough flash space, and you had the Stability Control ABS, and the CAN was featured enough and fast enough to add a real time communications channel, you may be able to add it. It would be what I'd class as a very challenging implementation *IF* you could get the source code. But no way on this earth would you get insurance on it.
On a 3.0l, consider it virtually impossible.
As said earlier, if you must have it, buy a car with it.