i couldn't find any unseasoned/unseasoned nori in the 'regular' grocery stores around here, but found a couple at the asian market.
not being versed in the lingo, near as i can tell from the packaging, the brand name is 'Korean-squiggly line-straight line-squiggly-squiggly-circle-slash-exclamation-point'.
i think the hassle w/ roasted nori is that if it's roasted, it's more likely to have had additives/seasonings added during the roasting process. if you can determine that isn't the case, i don't think it being roasted is itself a deal breaker.