>>25038754In terms of late game
Shinki from Makai
Sariel from the Hakurei Cave.
Yukari from Muenzuka or Yakumo Household
In terms of encounter rate <5%
Flandre from Scarlet Devil Mansion
Suwako from Moriya Shrine
Yorihime & Toyohime from the Bamboo Forest Secret Area
Sukuna from Route 1
Yumemi from Route 2
Nue from Route 3
Mugetsu & Gengetsu from Route 8
There are some others but just pick your favorite