If you're using frozen clams, they can still be completely respectable, just look for something quality that was, ideally, frozen when still alive, and thaw them before baking. Frozen clams will ...

Shijimi can be frozen and stored after the sand is removed. When using frozen clams, just plunk them directly into boiling water. "Hatcho" miso uses soybean "koji" fungus matured for a long period.