Just as a silly exercise to see if it's possible to bend the Gatherer to do our bidding, I thought of a way to avoid *some* of the extraneous matches. We could change our query to say:
Name contains "Waxing Moon"
Name does not contain "b"
Name does not contain "c"
Name does not contain "d"
Name does not contain "e"
...
<every other letter that isn't part of Waxing Moon>
But a) that would be ridiculous to implement and b) it wouldn't cover cards like "A Waxing Moon" or "Waxing Moon Man" because they use the same letters.