A few modifications to make to the original post:
C) Dragon/Ghost (aka Dragon Ball):
Resisted by: Dark/Fairy, Normal/Fairy, Steel/Dark, Steel/Normal
Perfect Third Type Coverage: Fire, Water, Electric
Steel/Dark should be underlined because of Bisharp.
F) Dragon/Water:
Resisted by: Steel/Water, Steel/Grass, Fairy/Grass, Fairy/Water, Fairy/Dragon
Perfect Third Type Coverage: Ghost
Fairy/Grass should be underlined because of Whimsicott.
B) Dragon/Electric:
Resisted by: Steel/Electric, Steel/Ground, Steel/Grass, Fairy/Grass, Fairy/Ground, Fairy/Electric
Perfect Third Type Coverage: Ground
Same as above.
H) Fairy/Electric:
Resisted by: Poison/Grass, Poison/Ground, Steel/Grass, Steel/Electric, Steel/Ground, Poison/Electric, Fire/Ground, Fire/Electric, Fire/Grass
Perfect Third Type Coverage: Ghost
Fire/Electric should be underlined because of Rotom-H.
J) Rock/Fighting:
Resisted by: Psychic/Ground, Psychic/Fight, Ghost/Fight, Ground/Poison, Poison/Fight, Fairy/Fight, Fairy/Ground, Steel/Ghost, Ghost/Ground
Perfect Third Type Coverage: Fire, Water
Claydol is Psychic/Ground and Golurk is Ghost/Ground.
K) Ghost/Poison:
Resisted by: Dark/Ground, Dark/Poison, Dark/Rock, Dark/Steel, Normal/Ground, Normal/Poison, Normal/Rock, Normal/Steel, Ghost/Normal
Perfect Third Type Coverage: Ground
Diggersby is Normal/Ground.
L) Dark/Water:
Resisted by: Dark/Grass, Dark/Water, Dragon/Fairy, Dragon/Dark, Dragon/Fight, Fairy/Water, Fairy/Grass, Water/Fighting, Grass/Fighting
Perfect Third Type Coverage: Fairy
Azumarill is Fairy/Water and Whimsicott is Fairy/Grass.
M) Dark/Ground:
Resisted by: Grass/Dark, Grass/Fairy, Bug/Fairy, Flying/Fighting, Bug/Dark, Flying/Dark, Flying/Fairy, Fighting/Bug, Grass/Fight, Hydregion (ability)
Perfect Third Type Coverage: N/A
Togekiss is Flying/Fairy.
N) Ghost/Poison:
Resisted by: Steel/Normal, Steel/Dark, Normal/Dark, Normal/Ghost, Normal/Ground, Normal/Poison, Normal/Rock, Dark/Ground, Dark/Poison, Dark/Rock
Perfect Third Type Coverage: Ground
Again, Diggersby is Normal/Ground. Also, you listed Ghost/Poison twice. Remove the first one, not the second one, because the second one has Normal/Dark where the first one doesn't.
Sure, Diggersby and Whimsicott are gimmicky, but shouldn't they still be considered as far as type combinations go?
Also, using the statistics of Flying Press on
http://www.serebii.net/games/typecompatibility.shtml, I discovered that Flying Press + Rock has 8 resistances (though it's worse than Flying/Fighting, it's still something to note). Here's a list:
Flying Press / Rock
Resisted by:
Ground/Electric, Steel/Electric, Poison/Ground, Poison/Steel,
Psychic/Ground, Psychic/Steel, Fairy/Ground,
Fairy/Steel
Perfect Third Type Coverage: Ghost (not accessible to Hawlucha, though)
I might be missing something. There might be a better coverage move with Flying Press. I ignored types that have a common resistance with it (Poison and Bug are resisted by Poison, Ground is immunified by Flying, Dark is resisted by Fairy, Normal is immunified by Ghost) and only limited myself to Hawlucha's movepool. If anyone has a counterexample, please let me know.