There are two ways - using the spirit touch ability (which is, I believe, the third level of Auspex) or paying a merchant to identify them (most of the shop keeps can do it).
True, but in case you won't find any (which is quite possible since items appear randomly), you can go to the gipsy woman's shop and buy a few. That is if you can afford them, i found it fairly difficult to accumilate a decent amount of cash in the early stages of the game.