For monsters, just as a guess from plundering the MTG wiki (I will do the white now, and the other colors later, see
https://mtg.gamepedia.com/White#White-aligned_tribes):
Firemane angels (angels of vengeance)
Angels of despair
I am not sure if Serra angels are different enough from MM angels to get separate stat blocks
Archons (kind of like celestial knights, some of which are one being with their mounts, probably more LN than LG, but Arcadia could use some outsiders too)
Avatars
Owl Avens (when your pet owl is a better wizard than you are)
I don't think the Phoenix is different enough to get a separate stat block
Ditto the Roc (what, the Roc says "know your role jabroni, I will lay the smack down if I don't get my own block")
Maaka (giant six-eyed cats)
Don't know if giants are different enough to rate separate stat blocks
lammasu (more D&D shedu)--I haven't included any "almost extinct on Ravnica" monsters, but I am making an exception in this case
I don't know if the Pegasus is different enough to rate a separate stat block
I don't know if the Ceratok is sufficiently different from a rhino to rate a separate stat block
Wood version of a Caryatid column
the spirits seem like they could be handled by the ghost stat block
Moroii (psychic vampires)
gargoyles with a thunder attack
magic resistant griffins (mounts, can anyone say find even greater steed spell?)
Thrulls seem like they could be handled with the zombie stat block
There are some zombies with weapons surgically attached to their bodies