You might have sold them, you might have thrown them away, or you might have given them to different Pokemon. You might have used the move Fling and gotten rid of your item.
This would be what would've happened with your Macho Brace. If it was a Berry, it could have been removed by a foe's attack, or it could have been consumed by your Pokemon. Any Gems also would have been consumed. Same with a Bulb or Battery. Air Balloon would be removed if your Pokemon was hit by an attack. Also with a Berry, you could have used Natural Gift and it would've been removed.