I spent over three hours flying around Northrend looking for an unborn val'kyr. No luck
I then opened the 60 pet bags I'd squirreled away for today hoping for better luck with the stones. Out of the 60 bags I got:
12 mini pet biscuits
18 magic pet biscuits
51 pet bandages
+ tons of other vendor junk
So roughly a 1/6 chance on the stones from this small sampling. Although 3 of them were found in a row (no time to build up the 'bonus chance'). So again, not sure how accurate it may or may not be. I'm hoping others saved up as well so we can get a larger sample size to compare.