I rushed it Wednesday right before the matinee and got a ticket. I'm pretty sure they only give rear mezzanine and I'm sure they will have tickets right up until the show starts. You can't directly call a broadway box office, assuming that's what you meant by direct number.
It will not be sold out. It has been on TKTS and people have got rush tickets before. When I went they didn't have rush for that day, but you can get a rear mezz seat for the same price. And I actually like the view from the mezz because you can see everything and nothing is obstructed. And I think that is where they put the rush seats anyway. I doubt you will have a problem and enjoy the show. It is incredible!
"A well-rounded performer will listen to all kinds of music. I like classical, Middle Eastern, and rock a lot." -- Patti LuPone
You really have no need to worry. Osage never sells out (close, but the theater is a barn), and with a snowy day like tomorrow, your chances for a great seat are very high.