Yes, quite a few of us would be in Japan right now, or preparing and packing in order to be there next month.
nutwpinut ’s location in Fussa is particularly poignant to me as being at the nearby Showa Kinen Koen is such a family tradition for us in the Spring. LapChild not being with her grandfather is a tremendous disappointment for us, then again, not being with my parents brings us sadness too, but Spring really is Ojiisan’s time. Nevertheless, it’s good to learn here that there is food around, he’s a widower, does cook for himself, but doesn’t have the range and experience my own parents have and I would be worrying if Tokyo was experiencing the same problems London is.

cowie Sushi. Nigiri sushi is something I hardly ever make. LapChild (like SOO many kids who have been introduced to it at the right age) is a Nori Seaweed monster, LOVES nori, so I never really venture past norimaki and temaki sushi styles. You’ll hear that norimaki is the hardest of the sushi styles for an itamae/chef to master, that may be so, but it’s also the style where they need to somehow show excellence when many Japanese home cooks have a degree of competence - that must be a challenge.
But I’m going to assume you have no nori and focus on the salmon - I would never prepare frozen salmon to eat raw.
Two options
1 chirashi sushi (a very venerable style of sushi - when I go see family near Sendai for the Sakura season, a big plate of the most beautiful chirashi sushi will be on the table*, they don’t make nigiri sushi either, we go out for that)
2 onigiri - it’s fantastic with salmon.
Both options are great with fish eggs of any kind.
For chirashi sushi, if you can’t get sushi vinegar you can make your own, involves heating a mild vinegar to supersaturate sugar and sugar in it and then cooling it quickly so the vinegar doesn’t continue to evaporate.
For both options, main thing is getting the rice right - no need for a rice cooker. Any pot with a sealable lid will do (you can seal holes with paper, sarin wrap/cling film, foil, anything that stops stew from escaping). Will happily give a full walk through if you or anyone else is interested - needs to be a short grain rice.

* an example of that home cooked “sushi”