All your existing Tags can be assigned a corresponding fitout. You edit those by clicking on the tag name in the manage fitouts screen and then click-click (not click-drag) like you would for any equipment screen to mock up the fitout.
Likewise, Faction Inventory has the manage fitouts for Faction-owned NPC tags and those fitouts.
As far as I know there are no bandit fitout lists in the rules section. There are no rare fitouts as all fitouts have similar chances of occurring but some fitouts do have rare gear.
Rare gear meaning items that have been restricted by those that produce that specific item or items that can only be acquired through the bandit drops. Nightstingers, X-45 Sniper Rifles, Heavy Battle Armour/Helmets are examples of gear that are restricted but can be dropped by bandits while Force Detectors and Clone Trooper Armour/Helmets can only be acquired via bandit drops.
BARC Trooper Armour/Helmet, Mandalorian Armour/Helmet and Republic Commando Armour/Helmet was given away during Red Scenario's or Admin events that occurred quite a few years ago I believe.
Only a few sets were given out/earned so they are extremely rare and the only way you can acquire them would be to purchase, kill or swindle them away from people that do own them...extremely unlikely.