There are a total of 47 blue prints located during the single player portion of the game. Of these, 2 of them create 3 variations.
These are generally found as the little blue markers on the map (which can be made visible in each of the safe house after unlocking them from the vendor).
You also get a blue print after each case up until case 5. However half way through case 5 you will hit a point of no return. So if you have all blue prints except for one melee blueprint at that point, don't worry, you get the tripod zapper blue print for completing case 5.
All blue prints for this achievement are obtainable in your first playthru. Actually, if you have them all you will unlock this achievement before case 5 achievement.
POSSIBLE GLITCH
As warned by others, although i did not run into this problem, it is best to unlock this acheivement before playing MP or at the very least, before picking up any of the MP blue prints as this has been known to cause a problem and screw this acheivement.