So your best bet is to farm them in the ruins outside of Alfornada in South Province 6 at night using auto battle. Use a lvl 3 ghost type encounter power sandwich. All you need to use are 2 red onions and 2 of any herbs mystica. For lvl 2 boost, use 2 herbed sausages, 4 potato salads, and 1 vinegar. U can also use the Ultimate Vegetable Sandwich. Outbreaks of Sinistea are also helpful as well.
Don’t trust me with the sandwiches, there are also YouTube videos on how to make the sandwiches