Meta-Alloys are a special commodity in-game that can be used to unlock certain engineers, special modules and even fed to Thargoids. Here are a few different methods to collect Meta-Alloys.
Despite what some people say, Meta-Alloys are NOT CAUSTIC and will NOT deal damage to your ship if you carry them around. However, if you are scanned by a Thargoid Interceptor while carrying them, they may make some different noises, but ultimately they will not attack you.
Thargoid Barnacles are planetary surface sites that can be used to gather Meta-Alloys by shooting down the Large spikes that grow at these.
It is possible that these sites can be depleted so you must make sure that you are visiting a site that is NOT depleted when looking for one.
Here is a link to CMDR Panpipers barnacle spreadsheet, this can be used to find ripe barnacles and also sites that can be used to gather materials too.
Once you find a Meta-Alloy spike, you can break it and re-log the game to make it spawn another Meta-Alloy.
In the area surrounding Thargoid Surface Structures you can often find 2-3 barnacle spikes containing Meta-Alloys. These can be broken for a constant supply of Alloys and also do not deplete.
Non-Human Signal Sources
When dropping into a Non-Human Signal Source [Threat 5-7] there is a small chance a Meta-Alloy can be found floating in the instance. Beware, if any Thargoid Interceptors are present, they may try to collect it before you get a chance to scoop it up.
You can visit a Thargoid Barnacle Forest. Barnacle Forests are special barnacle sites with many barnacles, unlike normal barnacles, these do not deplete and will always have fresh ripe barnacles available.
A few well known forest sites:
Hyades Sector AQ-Y d81 C 2 at 9.2924, -153.9815