The Memospheres in Dem, Mea and Holla drop from the Crag-specific monsters and their NM counterparts; the Memosphere in Vahzl drops from those same three mob types as well as the three NMs. The Crag-specific monsters in Dem, Mea, and Holla spawn on all 4 floors and are a little more difficult to kill than the other monsters on the same floor; the ones on the first floor can be killed solo by some jobs, and duo by most. (As an example, a WHM/NIN with an Adventuring Fellow set to Stalwart Shield has no trouble with them.) It's been reported that a single party can kill the NMs in all four zones, but your mileage may vary.
Once each person who wants the map has a Memosphere, it's time to go looking for the ???.
There are a total of four places the ??? can appear in each Promyvion zone. In Promyvion Dem, Holla, and Mea, there are three ???s on the 4th floor and one on the 3rd floor. The 3rd floor is split into two separate pieces, so if you don't find the ??? on the 3rd floor, it may be necessary to go back to the 2nd floor and kill a different Memory Receptacle to get to the ???. For tips on dealing with the Memory Receptacles to climb each floor solo, see the Shadows of the Departed article.
In Vahzl, there is one ??? on the 3rd floor and there are three on the 5th floor.
The ??? locations are typically in places where clusters of monsters will spawn. You can either have your group clear the area before trading, or in a solo situation you can use the macro /item "Indigo Memosphere" <t> to trade the item without use of the trade dialogue window. When you trade the item successfully, all monsters will lose any enmity they built towards you and won't aggro for a few seconds, which gives you enough time to run to safety.
|Zone||Memosphere||Dropped by||??? Locations|
|Promyvion - Dem||Beryl Memosphere|
|Promyvion - Holla||Teal Memosphere|
|Promyvion - Mea||Indigo Memosphere|
|Promyvion - Vahzl||White Memosphere|