There used to be an upgrade kit, 9166579, which included the gauge and sensor. However, this is long-since discontinued. You might strike lucky and find a new old stock kit, but more than likely you'll be looking to pull a gauge from a breaker. The sensor is still widely available new.
The gauges were standard on the top-end CD spec cars, but often suffer LCD bleed. It's really a case now of keeping an eye open on eBay, Marketplace and similar.
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