Different cores have different programs. Maybe you do need some specifit core to promote your certain attribute, or you need some cores to swap a No.0 Core in the R & D Center, but you can't get it from the enemies. What to do?
The Core Dealer (457,819) on the Steel Warship will help you out.

You can just spend 2 Zero Points to buy a core from him. But each day you can only buy 10 cores at most.

VIP player and Military Badge owner can buy more (System will tell you how many cores you can buy at the moment). What's more, the Military Badge owner can claim one core from the offline training center each day.