You can get Nori sheets from the LFS or even from the grocery store in the Asian food section. If you do get them from the grocery store, make sure you get the plain ones, not the seasoned/salted/flavored ones.
/flame suit on
I know there are people here that feed veggies and fruits to thier tank (I believe BL1 is one of them) - but in several places, Bob Fenner sugguests this is not a good idea, as terrestrial veggies dont have the same nutrients that marine veggies do. I think you'd be okay for a while on other veggies, but if they need seaweed (such as tangs) you really should be feeding that to them
/flame suit off