Rare Recipe books or at other times Recipe scrolls can be found by searching for randomly spawning Treasure Chests (only in dark areas, and on the surface it has to be night as well) or either killing or taming and then harvesting from certain Creatures that will also drop rare Recipes.
A list of all rare recipes can be found in the main article Recipes.
Recipe Books can be collected to be learnt by right-clicking them, after that their Recipe will be added to the Crafting Menu. After learning a rare Recipe, it will keep being available in the Crafting Menu on all game worlds, even on those with the world option "world bound recipes" activated.
If you find a Recipe Book and already know the according recipe on it, a check mark will be shown over the Recipe Book icon. You can still collect spare Recipes and later trade them with other players on the world where you've stored it. Recipes can be dropped in a player bag and collected by other players, but only on the same world. So if you want to learn a rare Recipe from other players, you'll have to visit their worlds.
Nowadays, Recipe Books and Recipe Pages are pretty much the same. Books aren't rarer than Pages/Scrolls anymore (they were back in Early Access).
One rare Recipe - the one for the Super Extractor can only be obtained from Things - these are very tough and aggressive creatures that spawn on corrupted rocks in darkness, most often on the Corruption layer deep underground.
Rare Recipes have to be learnt in order to add the crafting recipes to your Crafting Menu. To learn rare Recipes, right-click on them in your inventory, or drag them with the mouse (left click and hold) over the model of your player character to the right side of the inventory.
While Wood Treasure Chests with the lowest tier will only spawn randomly during night-times on any surface block in complete darkness (without any artificial Lightings nearby), other Treasure Chests will spawn randomly during the whole day on specific blocks from underground layers in darkness. They can be made to spawn on player-made artificial biomes too.
Treasure Chests, like Creatures, will only start to spawn within a certain radius around player characters (also underground and/or up above).
Stone Treasure Chests spawn on blocks of the Fossil layer (accessible through shallow Caves, like on Bedrock or Limestone. Obsidian Treasure Chests spawn on blocks of the Stalactite layer like Siltstone or Stalactite. Iron Treasure Chests spawn on blocks of the Lava layer, like Hardened Lava or Igneous Rock. Diamond Treasure Chests spawn on blocks of the Corruption layer and on any kind of blocks that have been corrupted by players.
3 rare Recipes of low tier can be looted or pet-harvested from Trogs, Dustevils and/or from Dried Leafies. High-tier rare Recipes can be obtained from Things, Silver Keepas and Golden Keepas, low-tier Recipes can be obtained from ordinary blue Keepas, mid-tier Recipes too, but only when harvesting from tamed Keepas as Pets.
All of these recipes will "carry over" to new/other game-worlds just like all the recipes that you have bought from the Store, even if you deactivate the according option in the world-menu. So currently you will start on new worlds with the usual starting recipes plus all Store-bought recipes plus all of the rare Recipes that you have already collected and are listed in your crafting menu.
For more details and a list, please refer to the article Recipes.