I dont have my hand in this project anymore but I dont think it would cause any harm for me to answer. The way I see it is this. Your character is capable of hearing about any of those items throughout the course of their life either while adventuring, old family tales, some rambling bard in the inn, ect. Or if your character is the type such, as a bard, that would have some experience in such legends and tales then it is fair to assume that you've learned of it through companions or research. Though seeking the knowledge through a gm run NPC wouldn't be a bad thing.
When it comes to finding the item. That would depend on the item itself and whether or not it was actually put into the game. If it was I dont see any reason why you couldn't find it but I find it doubtful unless a GM put it there for future quest possibilities. Either way it is always best, I think, to work with a gm in this type of case simply because the potential stemming from items of this caliber are always tremendous.