This is obviously an extremely old post, but still worth answering for anyone who might be reading as this question still comes up when you Google "DADGAD strings":
A lot of players do play just fine with a normal set of standard 12s or 13s tuned to DADGAD (11s tuned down might feel a too floppy for an acoustic player, and I've found them a little more liable to break when strumming with a pick, and have never had any issue like that on 12s).
However, preselected sets tailor-made for DADGAD have become a bit more common, so you don't need to go out a create a custom set which can be more expensive, or worse, throw out a whole pack's worth of strings, which is the worst case scenario imo.
D'addario make a set of their regular phosphor bronze acoustic strings especially for DADGAD, called EJ24. Given how widespread the brand is, these seem to be quite readily available in music stores despite being a bit niche.
The only other brand I see making them are these by Lowden, though I have no experience using them so I don't know what they're like.
Couldn't find many other similar sets out there myself, but I'm sure a few other brands may do them.