There are fifteen Mystical Tome Materials. Each one is required for at least one Mystical Tome, and some are more common than others.
Carbon Steel - This item is crafted from 50 Iron Ore at a Hellforge.
Dew of Herbs - Dropped by Corrupt Slimes, Gastropods, Illuminant Slimes, Toxic Sludges, Floaty Grosses, Crimslimes, and Rainbow Slimes at a 10% chance.
Dew Orb - Dropped by Snatchers, Man Eaters, and Angry Trappers at a 12 in 100 chance.
Element Diamond - Dropped by Ichor Stickers, Chaos Elementals, and Ice Elementals at a 10% chance.
Element Dust - Dropped by Ice Tortoises and Giant Tortoises at a 10% chance, and by Flying Fish, Vultures, and Unicorns at a 1 in 5 chance.
Fine Lumber - Crafted from 60 of any type of Wood at an Anvil. Makes 15.
Gravel - Crafted from 10 Stone and 20 Silt Block at an Anvil. Makes 15.
Mystical Claw - Dropped by Cave Bats and Jungle Bats at a 1 in 7 chance and by Giant Bats at a 1 in 11 chance.
Mystical Totem - Dropped by Wyverns at a 50% chance.
Rubybead Herb - Dropped by Harpies, Cave Bats, and Giant Bats at a 1 in 6 chance, and by Jungle Bats at a 1 in 12 chance.
Strong Venom - Dropped by most Jungle mobs at a 10% chance. Also dropped by Black Recluses at the same chance.
Sandstone - Crafted from 10 Sand and 10 Stone Blocks at an Anvil. Makes 5.
Mysterious Page - Crafted from a Spell Tome at a Bookcase. Makes 2.
Scroll of Tome - Dropped by the mech bosses. 1 in 3 chance.
Dragon Orb - Crafted with 1 Element Dust, 3 Element Diamond, 7 Rubybead Herb, 3 Dew Orb, 5 Strong Venom, 1 Mystical Totem, 3 Dew of Herbs, and 2 Mystical Claw at a Tome Forge.