Alloy nipples are not the sturdies things - if it is the nipples that are breaking - get some brass ones.
I would recommend double butted spokes from DT Swiss. The way you process steel has a lot to do with how stretchey/strong/brittle it is - so going with a good company is worth it.
Also - there are a few websites that let you buy individual spokes - so you don't need to buy a whole box:http://www.cambriabike.com/
Is one of the companies that does that.
I lost a few spokes last year after my derailleur decided that shifting in to the wheel was a good idea, and was able to by 8 spokes to replace them.