The closest location for Memory Alloy is near the B2 elevator entrance. First, get B2 access from Gideon at Two Brothers Weaponry. Take the elevator from 1F to B2. Go northwest to the large room where you'll encounter a giant robot (see image). Defeat it for a random chance to get Memory Alloy. You'll have to leave the Junk Heap and fight the robot multiple times if it doesn't drop.