I hear you about not being able to get fresh fish can be used for sushi. It is sad.
Besides your ideas, how about "chirashi-zushi"? I thought it would be an excellent party dish; it's visually catchy, you can substitute fresh fish w/ shrimp, smoked salmon, and other cooked seafood, and it's very easy to make. It is known as a spring dish, but who cares.
I found a recipe on the website below.
How to Make Japanese Scattered Sushi
Chirashi-zushi
Ingredients:
* 3 cups sushi rice *rice and sweet vinegar mixture
* 4 shiitake mushrooms
* 1/2 cucumber
* 3/4 cup dashi soup
* 3 eggs
* raw tuna/salmon slices
* boiled shrimp
* 2 tbsps mirin
* 1 tbsp soysauce
* 3 tsps sugar
How to Cook:
1. Prepare sushi rice.
2. Put dashi soup, mirin, soysauce, and sugar(2 tsps) in a pan.
3. Add shiitake mushrooms in the pan and simmer until the liquid is gone.
4. Cool the simmered shiitake mushrooms and slice them thinly.
5. Beat eggs and add sugar(1 tsp).
6. Pour one scoop of egg mixture into a frying pan and make a thin omelette like a paper. Make a few sheets.
7. Cut the omelettes into thin strips.
8. Cut the cucumber into thin strips.
9. Serve sushi rice on a bowl or a large plate.
10. Spread shiitake mushrooms, cucumber, and omelettes strips over the rice.
11. Place raw tuna/salmon slices and boiled shrimps on top of the ingredients.
12. Serve pickled ginger on the side.
*Makes 4 servings **It should be decorated colorfully.