Name of State: South African Republic
Name of Representative: Francois du Toit

How do you make Tardis plural?

Tardii???

Having stumbled across this, I feel obliged to lay that question to rest.

The word Tardis is constructed as though it were a first-declension Greek word ending in -ης (-is in modern Greek pronunciation, -és in ancient Attic Greek). If we were to assume a modern Greek origin, the plural would simply be Tardes (the final -es rhyming with days). An ancient Greek origin would yield a plural of Tardai (the final -ai rhyming with sky), but a distinct dual (used instead of the plural to denote two of something) form of Tarda.