Quick tip: Find gun-related parts on AliExpress using "Recommended" section of another gun-related part.

My understanding is that Ali has removed lots of gun-related parts (FCG, springs, solvent traps,...)

Some sellers seem to still sell them, but may not use the same keywords or pictures to avoid detection. So they're harder to find.

The trick I use is to go on some gun related part page (ex: 'Hydraulic tube', the ones that are used to make DIY barrels), and then scroll down to the "recommended" section.

The way it works, is that is shows things people who bought the hydraulic tubes also bought. As these are often used to create FGC9s, you'll find that people who bought them often bought 'Interesting' things, ex: mag springs, FCG springs, reamers, rifling buttons,... The process can be iterative: you can click the rifling button and go to the recommended section to find more stuff.

Full FCG and Solvent traps are hard to find these days though.

Hope this helps, Ali has been a reliable provider for non-US people.