Rusted weapons can be obtained from 2 places:
- Proto Bahamut (usually 1 per kill, but can be replaced by a flip chest)
- Angel Halo (Archangel Cores or lvl 17 Angel Cores, rare)
Both Revenant weapons and Bahamut weapons require a level 75 Rusted weapon, meaning a fully uncapped Rusted weapon. Generally, players will need to run Proto Bahamut and Angel Halo dozens, if not hundreds, of times for other drops, so they will be able to easily fully uncap some, if not all, types of Rusted weapons.
Because there is such high variance in Rusted weapons, it is also not uncommon for a player to not get enough, or any, copies of the specific weapon they need. Steel Bricks from the casino are a viable solution if you have bad luck or are just impatient to craft your weapon.
Extra Rusted weapons can be used to upgrade your crew's airship.