Website and data research by 101Leafy.
Deep Map
ディープマップ · Map
Tower of hell: Deep Hole map
Sells for 100
Versions: Shiro no Sho
No shop sells it, no chest holds it, no enemy drops it, and 101Leafy has not found a story event that gives it.
Shin Megami Tensei Wiki by 101LeafyAll Demons Index