Distressing one map is fairly straightforward (start with good linen or rag paper, crumple a bit, fold a few dozen times to get relaxed fold lines (folding almost but not quite in the same places each time), spill one or more kinds of tea on it for staining, bake in an oven to get a more brittle and aged paper, whacking repeatedly and possibly hitting it with sandpaper to distress the edges). Doing them in bulk is something I wouldn't want to contemplate. It's probably much easier to distress one, scan it, and print multiples of that.