DP seems to be more abundant after you start seeing the Antibodies throughout the world (so, around Phase 3). Personally, I got this in XP Shell going for a True Ending, but for the most part, you can easily grind this out for one Reyvateil using either Moebius Factory or XP Shell. The DP cap is 99,999, and you can get anywhere from 20 to 2000, depending on the fight you come across in Moebius, or generally around 1k to 2k from XP Shell.