There aren't too many and they have a high chance of dropping a rare core crystal so it is recommended to find all of them. (thetech52.com)
Players who've purchased the game's expansion pass will receive another DLC items pack, which contains eight Legendary Core Crystals, upgrade parts for Poppi, and other useful items. (gamespot.com)
The first pack, «Support Items for Your Journey,» dropped right on launch day and includes 50,000 G, 3 cream orange paratha, 10 silver cylinders and 5 common core crystals. (goombastomp.com)