Ritual skills are indeed learned through quests, but the quest givers need not be sages. Many quests have a random type of reward, where a new ritual is one possibility, but the rate at which you get new rituals is rather slow, so not getting any for half a year doesn't sound off (I think my character has gotten 3, including a "fixed" one when the character has been deemed ready, in a bit over 1 year).
The current system of pleasing the spirits seem to be in the need of balancing, as you can't sacrifice fast enough (due to the rate limitation) to keep them from hating you unless you essentially cease to catch small game. I'm not sure about fishing (haven't done enough to get any data), but it seems all general sacrifices go into a single pool shared between at least catching game, fish, and a summoning that requires a sacrifice. I'm not sure if cutting down trees count as well, but suspect it does, but eventually you're probably finished with your building projects.