I agree that Great commanders come more often than I'd like, or rather when I want something else, though the +1 str addition to any unit is nice enough that I don't complain. It's due to the national epic and a couple other wonders, I guess the ones I like just happen to give great commander points.
I do actually like the idea of a soldier specialist. Can it be made such that when you have a unit with enough experience (which you'd get from killing impossible odds or wiping out another civ eventually) stationed in a city, you can allocate a "Town commander" to add a defense bonus, +1 beaker, and +3 Great commander points?
If not, or if it is preferable to find a directly combat orientated method, I'll suggest that killing a certain number of units in one turn gives you a chance of spawning one. Perhaps an ever increasing number, like other GP point increases.