Yes there is a walmart, but only one actual grocery store, and it now stock frozen sushi.

Update: I shared this picture with my local gaming group, one of them went and picked up a tray.

He tossed it into the fridge and tried it this morning.

I had the first piece. It is supposed to be "Refrigerated Only" by the packaging, but honestly, with a fridge thaw, it tastes just fine. I've had plenty worse than that.

If I was not vegetarian I would give it a try. The closest place to get sushi to us is an hour drive.