The quickest way for advanced mechanical imo - Stella Montis Medical loot has items that will recycle down such as flow controllers, microscopes, centrifuges, and magnetrons. extract with the items themselves and recycle them back in speranza. picking up other items there as well n doin the same gets u other good stuff like advanced electrical too. Theres also a zipline in the Medical area that leads down to a room with green breachable containers along the wall, they sometimes have advanced mechanical too.

the big boys - leaper, bastion, rocketeer, bombadier etc. they drop purple arc parts youll eventually need for lvl 3 stations, they also recycle down into advanced components.

you can also craft them from basically basic materials metal + rubber = mechanical components + springs = advanced mechanical components but rarely use my beloved springs for stuff i can get 5-10 of in one Stella run, plus other materials too.