Ummm now I feel stupid as never even thought normal supermarkets would sell plain nori.i never seen it there but never looked for it though but next time I'm at tesco I will look ,I'm guessing it be in the world food Isle.You shoudlnt really struggle to get Nori suitable over here - Ive used the stuff from Waitrose, Tesco, Asda etc and all is fine. As long as there is no added ingredients and it is plain, with no added extras, seasoning etc. there isnt an issue using it.
Id still go to eBay to buy personally though. You'll get 500 large sheets for the price you pay for one packet of Ocean Nutrition.
FYI - Non roasted would be great and is availbale on the likes of amazon etc, but other than possibly being less nutritious (No idea if thats even true or why it would be) I dont see or have any issues feeding the roasted version. Fed it for years when i had my large tank and swore by it for colour.
Thanks