Had no issue with this, towards the end of the game I had about 90+ of everything but Prismere Dust and Essence of Fate.
- Focus on the stuff you have the least of, usually essence of fate and prismere, because by definition they are quite hard to come by.
- Find a location for each.
- Harvest them and write down how many you got starting from 1
- Go sleep in an inn/home bed for 48 hours
- Go back to location and harvest again, adding to the number you are writing down.
- Continue until you have 10 of each or you get the achievement.
You can essentially do this for all types of reagent. If you fast travel and have all the locations you need, it shouldn't take more than an hour.
Dragon Age:Origins + DLC, KoA:Reckoning, Elder Scrolls V: Skyrim, Fallout 3 + DLC, Assassins Creed, Assassins Creed II + DLC, Deus Ex: Human Revolution, Lego Pirates, Dead Space, Dead Space 2 + DLC, Majin & the Forsaken Kingdom
Stacking, Beyond Good & Evil HD, Deathspank, Deathspank: T.O.V, Banjo Kazooie.