Are there any tricks to help me find all the Animus Data Fragments?
Solution 1:
If there's one passing in your field of vision when you are in eagle vision, it will appear on your map. When at 50, you will receive a free map that show them all in your map.
Solution 2:
Actually once you go far enough into the game, they will start to appear on the map for you after you have obtained a minimum amount of fragments. IIRC, I was starting Sequence 6 (some time just after a major break in the story) with ~60 when this happened, though Shinrai confirms the minimum is 50. There was no map to buy.