By purchasing this item you can directly exchange 30 Platinum 30 for 3000 Salvage.
Beginning in Update 9.0 (2013-07-13) materials could be purchased directly from the market for Platinum.
These are based on opinions and may not be true. These should be viewed as advice for finding the materials until better facts are proven.
Carme (Mobile Defense) on Jupiter will possibly drop as much as 2,000 a run if you loot all of the containers and lockers.
Olympus (Disruption) on Mars can provide at least 2,000 Salvage.
Endless missions have a higher concentration of mobs and also contains a decent amount of storage containers and lockers, which also have a chance to drop Salvage.
Elara (Survival) on Jupiter, with a Nekros (Desecrate) and a Kubrow or Kavat with Animal Instinct and Scavenge, as well as a nice Slash AoE-weapon like Atterax or Scoliac (Or Ignis / Amprex, if you don't like Slide-Attacks). You can systematically go from room to room, and open most lockers and destroy all crates (Works best in Solo-mode). This method should net you about 600-1,000 Salvage per minute (Without a Resource Booster) until no lockers/crates remain.
Io (Defense) and Callisto (Interception) on Jupiter can net approximately 2,000 - 2,500 after each run to either wave 5, or round 1, respectively.