I know that Daisy, Bobbi, and Clarke have all tracked (on Clarke's suggestion) community events that are happening to guess where the next drop off will occur. They already know (thanks to Prompto? I think? Kira has been tracking a calendar) how many days tend to pass between each drop off.

So, a lot of the legwork is done there! It likely just needs to be revived as a direction, since the dream event in March threw a lot of people off.