Matcha Powder Substitute? Is there one For this recipe?

One idea: you might be able to scald the cream, add a teabag or perhaps 2 or 2 t. loose green tea if you have it in an empty Melitta teabag and let steep an hour or two. Then proceed with step one of the recipe. You likely won't obtain that lovely green and the flavor may be milder but it may be worth experimenting.