No Prep Adventure Path 2: Scrap City (Patreon)

https://www.kassoon.com/dnd/adventure/no-prep-adventure-path-scrap-city/ 

A new orc chieftain has risen to the top by eliminating the previous chieftain in a brutal battle, and since then he's been stockpiling smuggled magic stones. The stones are being used to create impervious war machines,  all in preparation for an all-out war against the kingdom. This all  comes during a delicate time, since the monarch has just come of age and  is assembling their council that will plot a new path for the kingdom.

https://www.kassoon.com/dnd/adventure/no-prep-adventure-path-scrap-city/