The Ohto Tasche looks like a possibility albeit smallish. I have XL-sized hands. The space pen is great because it is small, just over 9 cm closed, but in use with the cap is a full-sized pen at ~13.5 cm. I'm looking for something similar in a mechanical pencil, smallish and able to fit in a front pocket, but full-sized in use so that extended use is not painful.

Basically I'm looking for a pencil I can use comfortably in the field for extended periods, yet small to carry and as portable as the bullet pen. Capacity for many spare leads is also a plus.