There are some lava planets with neodymium or cobalt rubbles (don't remember exactly) that drop them after you drill them. Usually accompanied by meteor showers, so be careful, but it's the fastest method I've found.

You yet so me from the big base turrets, it's not a lot but it's something.

Honestly there is Soo much salvage to be had that I rarely run out of anything but bridges and matrices.

The cylindrical pieces of space junk in the debris clouds often have CPU extenders in them. I farm them for power coils, money, or the extenders them selves. There are also large and occasionally XL CV thrusters to be had. Also, until you get a master salvage tool retrieve them and break em down in a decon. But one at the junk station after you sell a couple extenders.

Note: go outside starter systems for T3 and T4s.

Buy a blasters at isi station and deconstruct.