I constantly tried to search in new chunks and couldn't find a single cell in three hours, even after asking the Pixelmon Discord if I made a mistake.
I than found that the best way to get them is:
1. going to a new chunk
2. staying afk for 10 minutes
3. seaching cells near you
4. repeat
The whole process just feels pretty boring and unintuitive.
I would suggest:
1. making them instantly spawn in when going into new chunks
2. give the cube a visual that displays whether the cells can spawn or are near you
3. make them a bit more common, you still need 100 cells and 5 cores and needet to craft the cube first