Having a hard time finding them
Converse with fellow players
Spheres can be got trading in 10* weapons and Units, those along with normal grinders you will find yourself rolling in just playing the game more at higher levels
If it's lambda grinders you need just keep doing Falz for now when ever he shows up
Grinders seem to drop frequently from enemies over lv 50. Especially during urgent quests that involve killing enemies to meet point quotas.
@Bl4h i don't know if it's because it's still in beta. But i can only trade 10 star weapons at the swap shop, it doesn't give me an option for grinders. And i have a TON of them