Ah, so you try to equip something the combatant isn't allowed to equip?
Well, yeah - that'll not show up, since the combatant can't equip it.
The available equipment of the combatant (either via template or a custom setup on the combatant) defines which equipment slots the combatant has and which equipment can be equipped.
I'd recommend to set up the available equipment to allow everything except the defined equipment or item types. Use the Exclude Equipment and/or Exclude Item Types settings for this.