Wasabi is basically a type of horseradish powder colored with spirulina. You could grate raw horseradish and use that and it would be raw. That might be similar to wasabi. But you usually eat such a tiny amount of wasabi that I wouldn't think it would be a big deal to eat it even though it's cooked, unless it is very important for you to be 100% raw.

You could make your own pickled ginger to go along. Raw ferment it, add a little beet juice to color it pink. I haven't done that myself, yet, but I've been toying with the idea. I know it's possible, and I'm pretty into fermentation these days! Hmm, speaking of which, think I'll go eat some of my raw dill pickles! :-)