I would agree with the previous posts. Farming stones via wild pet battles is very unreliable. I would get more stones from doing the tamer dailies and yes I do all 16 of them (17 when Darkmoon Faire is up). There were still days I would get no battle-stones from the bags but there were also days that I got as many as 5 stones. The only downside from doing the tamer dailies is that I also get too many Pandaren spirit pets and I don't know what to do with them anymore.
I also would like to note that that in one of my battles against Jeremy Feasel of the Darkmoon Faire, a battle-stone dropped. The stone dropped right after I defeated his team and did not come from the satchel. I am not sure now if defeating tamers also grants a chance for battle-stones to drop or that was a bug.