Item Finder:

To get the itemfinder u must have 30 pokemon in your dex. Then go to Vermilion city. Go to route 3 and then go upstairs in that building next to Silence Bridge where the Snorlax is. Talk to Oak's aid he'll ask you if you have 30 pokemon. Say yes.
If you are lying he'll know. If you have 30 pokemon say yes and he'll give you the itemfinder.

This is a list of items you can find:

Soothe Bell
Macho Brace
Leftovers X2
Sacred ash

Unknown item by the P.C in Vermilion
Unknown item in the underground tunnel.