You can special order doors at just about any height you like from most places that sell doors. I don't know the cost but it shouldn't be too much more expensive than the standard sizes.

If you get a real solid wood 6 panel door you can easily cut off 5 inches, divided between the top and bottom.

3 inches on the bottom and 2 inches on the top should look fine.

Do not mistake solid core for solid wood. A solid core 6 panel door is built totally different from a solid wood door made by a custom millwork shop. If you are going to paint the door, just get a solid core masonite door made to your custom size.