Just as a thought, if you're breaking spokes that is an indicator that all is not well with your wheel (duh, right?) By that I mean replacing a spoke means it wasn't tensioned properly in the first place and simply replacing a spoke isn't really fixing the underlying problem.
Or... maybe you're just really hard on wheels, but it sounds like they weren't built properly. (they also need to have the tension checked periodically, which you can guestimate by pinging the spokes witn your fingernails... they should all sound about the same tone on one side of the rear wheel.)