Question: how do you get masterwork cores in destiny 2?
Answer: Probably the best means of getting Masterwork Cores is to rank up with the Gunsmith to earn packages. ... 
The other method is to use a Finest Matterweave, as this is a guaranteed way to get a Masterwork Core. ... 
Finally, once a clan has reached Rank 6, completing a Weekly Clan challenge rewards a Masterwork Core.