Do you make 12 hole ocarinas?

12 hole ocarinas are problematic. Opening more holes to raise the pitch also allows the internal air pressure to escape. To compensate for this the player has to blow harder. However at some point the air-stream becomes turbulent and tone production stops. This limits the total range an ocarina can produce. 12 hole ocarinas exist right on the limit of what is physically attainable. Consequently implementing one leaves a maker with little freedom.

As the whole chamber oscillates the two sub-holes of a 12 hole ocarina change the playing characteristics of the entire instrument. To attain more range exponentially more air is needed. The pressure difference between the low and high notes increases dramatically and the high notes sound more airy.

Due to these pitfalls makers of 12 hole ocarinas frequently cheat. They tune the low A with a large reduction of breath pressure. While this does clean up the high notes it greatly reduces the volume of the low end. It also makes it difficult to play the low notes in tune. Eliminating the sub holes and reducing the chamber volume makes the whole instrument easier to play and sound better. In other words:

Regardless of how good a 12 hole ocarina is, the same design with a smaller chamber and fewer holes will result in a better instrument.

Pure Ocarinas does not and will not make 12 hole ocarinas. A 10 hole ocarina is more balanced over it's sounding range. The breath curve also becomes much easier to deal with. It's almost linear with a small difference in pressure between the lowest and highest notes. This makes the ocarina much easier to play in tune, especially in faster music.

If you want more range either play a multichamber or a different instrument. In a multi each chamber is responsible for only a small part of the total range. A double alto G ocarina overlaps the range that a 12 hole alto C attempts to create yet can sound every one of these notes without making compromises.