Unsure, possibly not. It's questionable dasani bottles are constructed with the same pressure tolerances as a regular PET soda bottle. (Probably, but you'd want to find burst test info, or if some else regularly uses them.)
PET is just the particular plastic material used. So the best would be to use soda bottles. I prefer things like old sprite/7-up over coke/pepsi unless I'm pressurizing a cola.
If you want to buy them new, I'm sure you can, such as
http://www.northernbrewer.com/shop/amber-500-ml-pet-bottles-case-of-24.html. Personally, when I think my 2 liter is getting too damaged and I don't want an explosive wall breach, then I just pick up another 2-liter of sprite, drink that (I suppose I could dump it down the sink) and reuse that for a while.
Chances are, some packaging person (like myself) would say, you know, we can save money by using less materials, thinner walls and less burst tolerance because these bottles don't need to be as strong as a soda bottle.
You can probably feel the difference too, when you squeeze an empty water bottle vs squeezing an empty soda bottle.
