I could see maybe defining the set of searchable items as those that:

Are not from an explore area, and are -either- unlimited -or- are limited, have the "least rare" status according to legendary awareness, and have level <= 40.

If you wanted to make it primarily useful to low-ranked characters, could filter out items from areas where the LOW end of the level range is >= some threshold. Say 45.

This would allow for items like the drow sub-commander's iron broadsword to be included in item search. It's limited, yes, but also fairly common.