Jane, as far as I can see, the mish of mish mash never appears by itself. In fact, the expression is almost always written as a single word, mishmash, or hyphenated, mish-mash. But in any case, mish doesn't seem to exist as a word in its own right. So I'm not persuaded it should be added to our word list.
Sorry about that - a mish is as good as a mile.
