Kavod HaRav: I checked the two closest supermarkets that deliver, and neither is selling (to my knowledge anyways) raw horseradish. Can I be motzei the mitzah eating prepared horseradish like from a jar with a reliable hescher? What about charoset?

No, we can't use prepared horseradish from a jar, because its taste is significantly changed by the beets, vinegar and sugar which they add (it's also been pickled in the jar, which disqualifies it). On the other hand, Romaine Lettuce, which is really the best halachic "maror" (even better than horseradish for it's easier to eat the required olive size!), is readily available in most vegetable stores, and just needs to be soaked a little in soapy water, rinsed and then checked well to make sure there are no worms there (that's true all year round). Regarding Charoset, it's really simple to make where most of the ingredients are found in most kitchens: dates, apples, wine, nuts/almonds, cinnamon (even if you leave out some of them, it's fine).