Buyable from Mechanical and Electrical Engineering Components booth
The Technoscavenger Brain is a common drop from low level robot mobs that is NoDrop (you can't trade it with another player). There are a few places where you can find them. Head to Athen Shire (west from West Athens) in the area around Trash King (1600, 1000) where you will find a junkyard full of Junkbot tech-scavengers, Buckethead Technoscavengers and Buzzsaw tech-scavengers that drop the brain. You must be careful to avoid the attention of the Trash King who is a tough giant robot and his pal Trash King Lackey next to him (they're social mobs so if they see you kill fellow robots they will attack). Stay on the north side of the junkyard and you should be safe. They also drop items for the shoulderpads quest if you haven't done it already.
You can find the same mobs in Greater Tir County (1650, 2200), and you can also find a large number of robots around Master Divenchy in Newland (900 x 860).