Your spokes are breaking from premature metal fatigue which would not have happened had the wheel been stress-relieved after the build. It has nothing to do with uneven tension. That would have caused an out-of true wheel which could or could not, have been stress relieved. An out-of-true wheel can last a long time, even though it is wobbly, if it had been stress relieved.
Stress relieving a wheel is apparently a black art and many mass-produced wheels are not stress relieved. Find a wheelbuilder who understands the process (but good luck in finding out whether he really understands) and have the wheel rebuilt with new, double-butted spokes.
Metal fatigues doesn't happen to all the spokes at once. Some go before others, but the fact is, in a situation like yours, they're all damaged and will go one after the other. Thus, just putting in a new spoke each time is futile and frustrating.
I doubt the spokes in that wheel are of a poor quality (cheese, as someone claims). Nowadays there are only four manufacturers of quality spokes and most wheels use those. However, a spoke is only as good as the installer's hand.