The most basic sort of salvage scanner are those in the Argo range. You can equip several of these and each will show you more wrecks to salvage in the current system. One thing to remember however, is that by default just having Argos on your ship you will only be able to scan for the wrecks of ships you yourself have defeated in combat at the current location. In order to see more wrecks you will need to equip another scanner in addition to your Argos, but what scan to equip depends upon what wrecks you’re looking for.
The wide spectrum T1 Scanner lets you scan the hole star system rather than just the current location, though note it’ll still only show you your own wrecks. The Wide spectrum T2 however will show you any wrecks other captains have created at the current location. The Guild spectrum scanner works similarly to the T2, but will show you the wrecks created by other members of your guild.
In addition to these scanners you can also equip a scan limit expander in your ship’s secondary weapon slot. This essentially works like Equipping another Argo scanner, and will expand the number of wrecks each scan shows you.
Note that specific alien versions of all of these scanners exist for use in The Expanse Galaxy.