Sometimes there's that specific item you really need, but you just can't seem to find it at the local shop. This is where the Crossgate importers step in. They can acquire anything but the rarest of items, although such convenience does have its price. Anything that might ever be available in the shop can be purchased at any time. The very reasonable rates are as follows:
Common in shop -- 3x normal price
50% chance in shop -- 5x normal price
20% chance in shop -- 8x normal price
5% chance in shop -- 12x normal price
Catacombs only -- not available for import
Anyway, I have no idea how hard this would be to implement, but it would be a really cool idea. Instead of just generating items randomly, the importers would filter through the entire list of XML items and display everything that isn't rare. Several price multiples might be too difficult (although one possibility would be a "shop" for each tier of rarity with different multipliers). The availability of any item at exorbitant costs would really be a great feature. Eventually, there aren't any good uses for large amounts of income, and this would be a good money sink. Plus there's the added benefit of not having to wait on just random chance if you really want something.