Same problem. No way to access seaweed.
It would be absurd if the only way to "get" seaweed necessary for a recipe that came with Snowy Escape is to do an activity that relies on a different expansion pack. Not everyone is going to have both and they should always behave independent of each other in that respect. This cannot possibly be intentional on the part of the developers. While the expansion packs generally mesh together, they always work independently as well. Not one absolutely relies on another (with the exception of My First Pet).
This has to be a bug.
Well the only foods that I know of which requires seaweed came with Snowy Escape. If you don't have that pack, such foods wouldn't even be on your sims' menu
