There are 35 Miracles in the game:

16 that can be bought from NPCs
11 that are found in static locations
5 that are made by transposing boss souls with Ludleth of Courland in Firelink Shrine
3 that are covenant rewards (Sacred Oath, Great Lightning Spear, and Darkmoon Blade)

This achievement can be earned in your first playthrough or across multiple playthroughs. There are missable Miracles tied to Irina of Carim, Yoel and Yuria of Londor, Ringfinger Leonhard and Siegward of Catarina, so be careful with their progression.

NPC and Divine Tome information can be found at the end of the solution.

Heal Aid
Sold by the Handmaid in Firelink.

Heal
Sold by Irina of Carim.

Med Heal
Sold by Irina of Carim after returning the Braille Divine Tome of Carim.

Great Heal
From the Hidden Manor bonfire, backtrack out into the watery area and stick to the left side. The miracle is on a dead creature at the base of the bridge where you entered the area.

Soothing Sunlight
Trade with Ludleth of Courland for the Soul of the Dancer.

Replenishment
Sold by Irina of Carim.

Bountiful Light
Sold by Irina of Carim after returning the Braille Divine Tome of Lothric.

Bountiful Sunlight
Trade with Ludleth of Courland for the Soul of Rosaria, which is obtained through Leonhard's questline.

Caressing Tears
Sold by Irina of Carim.

Tears of Denial
Sold by Irina of Carim after returning the Braille Divine Tome of Carim.

Homeward
Sold by Irina of Carim.

Seek Guidance
On a corpse in the cathedral of the deep. After running around the ledge where the giant tries to smash you, go down the hall, take the first left, and you'll see the item on a corpse on the other side of the room. Beware the slime above the corpse.

Sacred Oath
Earned by reaching rank 1 in Warriors of Sunlight (requires 10 Sunlight Medals). You earn a Sunlight Medal for every successful co-op session either as or with a Warrior of Sunlight. The knights in Lothric Castle have a small chance of dropping them, too.

Force
Sold by Irina of Carim after returning the Braille Divine Tome of Carim.

Emit Force
Given by Siegward of Catarina in Ithiryll of the Boreal Valley as part of his questline.

Wrath of the Gods
From the Profaned Capital bonfire, proceed to the toxic swamp area, then climb the ladder and work your way onto the roof. You can drop down into the building to land on a platform where this miracle is on a corpse.

Lightning Spear
From the Old Wolf of Farron bonfire, take the lift up to the area with a Stray Demon but go right and drop to a ledge that lets you get to the area behind the huge portcullis. The miracle is on a corpse in this area.

Great Lightning Spear
Earned by reaching rank 2 in Warriors of Sunlight (requires 30 Sunlight Medals). You earn a Sunlight Medal for every successful co-op session either as or with a Warrior of Sunlight. The knights in Lothric Castle have a small chance of dropping them, too.

Sunlight Spear
Trade with Ludleth of Courland for the Soul of the Lords.

Lightning Stake
Obtained by killing the giant worm in Smouldering Lake near the Demon Ruins bonfire.

Lightning Storm
Trade with Ludleth of Courland for the Soul of the Nameless King.

Divine Pillars of Light
Take the lift from the Grand Archives bonfire, then go outside and take the steps on the left to circle around onto the roof. Proceed until you reach a point where you can drop into the building. You'll land on a cage of sorts where the miracle is on a corpse.

Blessed Weapon
Sold by Irina of Carim after returning the Braille Divine Tome of Lothric.

Lightning Blade
From the Ithiryll Dungeon bonfire, go across to the opposite side of the large area, drop down a level, and go through a shortcut door that leads to a lift. Jump off the lift halfway down and the miracle is on a corpse.

Darkmoon Blade
Reward for reaching rank 2 in the Blade of the Darkmoon covenant. This requires 30 Proof of a Concord Kept, which are awarded for successful Blade of the Darkmoon invader kills. These "invasions" happen automatically when you are in the covenant if a member of the Way of Blue is invaded- you are summoned automatically to protect the host. It doesn't happen very often

They are also very rare drops by the Silver Knights in Anor Londo.