What do you want to be more random?
What troops drop? Add items with the troop editor.
What appears in the shops? Learn to code.
What troops use? Add items with the troop editor.
Changing the items will only change how often appear in the shop compared to other items (and their other stats of course)
You can use the item editor to increase the likelyhood that an item appears.
But what appears in each shop is based on the type of shop so samurai armor (for example) can appear in all armor shops regardless of culture. It might be possible to define new shops (like Khergit Armor Shop) but that involves some changes in the module system files.
Before i found a item_kinds1.text that fixed it.
in Native you only see the same things and not the other shields, armor,helmets
If i must learn a new program (item editor) then i rater pass