You would have to buy a new cluster assembly.
Looks like there is a salvage vendor in Texas that is showing one, but just not sure if it is a GT or not:
2008
Instrument Cluster(See also Speedo)
Mazda CX9 $Call Maz-Max, Inc. USA-TX(Houston) Request_Quote 713-896-8005 / 800-365-2193
Or you could just buy a new one from Mazda.
Either way, I think their MMDS machine could match the mileage on the digits to make sure it was the same.