The Solution We Used
The solution we finally ended up implementing is 3 fold.
A Sorcerer may buy additional shaping rituals with experience at the same cost as spells as long as they fit within the narrative. This explicitly does not apply to shaping rituals which would require a sorcerous relic that the sorcerer does not already own.
A Sorcerer may receive additional shaping rituals through story accomplishments without paying an XP cost, but the storyteller will treat this as receiving a 2-dot merit (or 4-dot merit for a sorcerous relic) for purposes of fairness of distribution of story rewards.
A Sorcerer with the appropriate skills may craft a sorcerous relic with the rules on p. 470.
Explanation
Further searching on forums found that at least some tables read the sidebar on page 466 to imply that sorcerers gained further shaping rituals entirely through story based actions.
While I think that is certainly a plausible reading, I didn't read it that way when I looked through it before. I read the sidebar simply as saying that the sorcerer wasn't limited to the archetype they started with when they acquired further rituals by taking the later sorcery charms.
Even if it was the intended reading that sorcerers gain further rituals entirely through the story, we didn't find that entirely satisfying. It meant that a sorcerer ready to spend resources was still confined by a story opportunity and it made it tempting for our sorcerer to try to hijack the story to engineer an opportunity to gain rituals. (Yes, a certain amount of that as a goal can be even be a good thing, but too much of it messes with the storyteller's plot and the spotlight, especially if they are chasing a specific ritual).
So, we allowed sorcerers to purchase them with experience in the same way as spells. Naturally this requires some story justification, just as spells do. But our table presumes that most things that do not involve "secret knowledge" are things that an exalted will either reasonably be able to either figure out on their own or find a reasonable source to learn it from during downtime.
In other words, Solar Circle spells, Sidereal Martial Arts, and the like require in-story work to locate a source of knowledge, but most things are just assumed to be available if you have the experience. As applied to shaping rituals, we assume that anyone can learn something equivalent to the "Student of Heptagram" shaping rituals (DB p. 309) with experience since equivalent libraries are available and it centers on study, but something like the rituals for Rashi's Tutelage (Lunars, p. 309) probably requires at least some real justification, especially for a non-Lunar.
We adopted the idea that some shaping rituals, especially those that involve singular acts rather than learning or training, can be gained through story without a further XP cost. This readily fits things like Pact With An Ifrit Lord (Ex3, p. 467) or finding a sorcerous relic. But at least my table tries to keep story based rewards that don't involve an XP cost relatively even. So, at this table, when a sorcerer gains a shaping ritual this way, it will usually be relatively close in time to the other characters gaining a roughly equivalent story based reward like a hearthstone etc. (Also, while not directly on point, I stumbled over this analysis thread which I found very helpful about the relative merits of the various rituals.)
Finally, there are explicit rules on creating a sorcerous relic and those of course apply.
