Let the Mage first be proficient in the use of Detect Magic.
He shall then form in his mind an image as perfect as possible, of the object desired.
Let him then send forth his attention as a broad beam attuned to the image of that object.
When he determines its direction, let him attempt again from another place so as to more accurately triangulate its location.
This spell is naturally more accurate at ranges less than a hundred yards, and the size of said object is only a limit to physically finding it once it is Located.