Can Gust target LeBlanc's Reflection token before it copies Harnessed Dragon?

Yes. LeBlanc's ability is a reflexive trigger: the initial effect only creates the token, then a second trigger transforms it into a copy. After the first effect resolves but in response to the second, you can Gust the token while it is still a Reflection token with 0 Might and has not yet copied the target's stats.