The key to a strong, long-lasting wheel is getting even spoke tension all the way around. It's possible to get a wheel perfectly "true" even though the spokes aren't tensioned evenly. This uneven tension leads to some spokes taking more of the load, which causes them to break... Then you take it in, they replace the spoke, and they have to tension that spoke unevenly again in order to keep the wheel true, which leads to it breaking, again, and so the cycle repeats.

The only way to solve this is to remove every spoke and start again. However, the key is finding somebody who *really* knows what they're doing with a wheel rebuild. You might want to start a thread and ask for forum opinions on who the best local wheelbuilder is. Tell him (or her...) that you want to completely rebuild the wheel.

Once they unlace all the spokes, they can take a look at the rim and see if the rim is undamaged / not-warped / etc. and take it from there. But I'd rebuild the wheel before bothering to get another one, as there's no guarantee a new wheel will have even spoke tension either.