I'm trying to come up with a metaphor that represents a collection of facts/notes around one thing. I've tried "deck" and "notebook" but they don't really work. Any ideas?
Well, to start with, to say they're a collection is to assume they're the same kind of thing, and that they are somehow connected, at least for future reference and retrieval. So some work has been expended to mark them.
Second, to say that they're "collected" around one thing is to say that there is some metaphorical geometric arrangement. Mathematically, the thing they're around implies a polar coordinate system, either 2- or 3-dimensional, with the "thing" centred at (0, 0(, 0)) and possibly a distance metric between the items in the collection and the center point, though not necessarily between the items themselves.
There are, of course, many more dimensions in collections like this than three.
Deck has several meanings, and I'm assuming it's the deck of cards sense you intend. That makes it a collection of 2-dimensional objects, which is OK, but without any center or connections, beyond four suits, two colors, ten digits (from 2 through 10 rather than 0 through 9), four capital letters (A, J, Q, K), and a slew of rules for playing with them.
You could also be referring to a Tarot deck, but that's just too obscure (though the category space is much much larger in Tarot, there aren't nearly as many games). And two-dimensional metaphors are most useful for writing, and there's damn little on either deck. So I can imagine that didn't work well.
As for notebook, there are way too many things that are called notebooks. You don't want a piece of all-purpose hardware, but that's the first thing that pops up these days when one hears a notebook. The original, pen-and-ink, variety is another collection of two-dimensional objects, this time with writing on them, which is an improvement, but linked only at one edge, with no centroid, no metric, no categorization, no interrelations -- and no index, a fatal flaw. So that's not surprising, either.
You might try some 3-D metaphors: database, box, sack/bag, shelf/ves, cabinet, etc.
However, since a good metaphor should match more than abstract characteristics, one can't go much further than this without knowing more, like
More literally, the CIA call theirs a factbook.