This is not uncommon. Many performance cars over the years have had tires custom spec'd for them. An example that comes to mind is the Bridgestone RE070, which for a while only came in exactly one size, because it was for the mid-2000s STI. It did come in another size a bit later when the GT-R started using it as the factory tire.

I want to say that the sixth generation Camaro SS 1LE also had a custom tire, though I think it comes in more sizes now.