I'll get back to you with a date for our next meeting for Christmas. I'll get back to you" is fine if a bit "fashionable" or lacking formality. Now the use of "for" is interesting, do you mean that the subject of the meeting will be Christmas or the timing of the meeting will be around Christmas or the date will be set by an email sent around Christmas? It is not clear. I might use "about" or "around" or "before".