This is your problem - you don't actually know how many you need (no-one does, it's RNG based). Staring at numbers leads to grinding leads to rage posts.
I know this will cause you to rage more but .. you need to chill and play the game rather than grinding. Build some rep locally so they'll give you the good missions with the mat rewards, then go off do some assassination missions (for instance) that give mat rewards. They require you to scan nav beacons to find targets - which means you can see if there are any HGEs in the system, kinda nice for getting mats, and then you get to kill the mission targets - who (now you are allied) will probably be Elite and drop yet more mats. Mix it up with some planetary scans which also reward mats and give data mats from the scans. While you are heading to all these mission targets scan any local ships ... for mats.
And leave the grinding for DTEA