Rituals and Buffy-verse

Player's Handook wrote: Rituals: Your book contains three 1st-level rituals of your choice that you have mastered.
At 5th level, and again at 11th, 15th, 21st, and 25th level, you master two more rituals of your choice and add them to your spellbook. Any ritual you add must be your level or lower.

WIZARDS AND RITUALS
A wizard’s spells are potent in combat and useful in a variety of challenge encounters and other situations, but the wizard is also the undisputed master of magical rituals.
As you gain levels, you automatically gain access to new rituals, but you can also buy new rituals or acquire them in the course of your adventures. Higher-level rituals let you seal or open doors, view places or people from a distance, or open portals to other places.

Ross wrote:Can we attain rituals other than having to be a Wizard. Was thinking about taking a feat to give me Ritual Casting, but seems ridiculous if we can't acquire new ones except by using the wizard’s Ritual Casting class feature? If we only have one Wizard we can only have at most 13 total rituals by 25th level. Can we purchase them, or say we spend the gold cost to research them in libraries and other places?

Ross wrote:...Can we purchase them, or say we spend the gold cost to research them in libraries and other places?