I buy 2-3 a day from spider, do the bottom row of spider's wanted bounties 3x each week and 3x gunsmith dailies. You can also farm nightfall ordeal which has a decent chance of dropping cores or prisms at the end. Right now, timelost bounty cycle with fractaline donation seems to get me 1 coure at least every other set from dismantles. All rights on related materials, logos and characters respectively belongs to Bungie, Inc. DESTINY 2 TM is in no way associated with MythicBoost. MythicBoost does not sell in-game items. MythicBoost provides in-game coaching services that will improve your skills, and help you obtain the items.
If you are solo player that doesn't like grouping up, you can do the 1020 Nightfall this week with randoms and easily get a 100K score. 100K seems to practically guarantee you a Enhancement Prism and Core. (Based on my runs anyway) You could LFG and do harder content but if you don't want to or you are too low power, this is a great way to farm.
The best place to farm for chests while completing Public Events is Titan. It is a smaller map, with lots of chests spawning, and two Public Events that are near each other. To collect Paradox Amplifiers, play Crucible matches and Heroic Adventures and Strikes.