That is going to be somewhat difficult.
From what I know Saturday and Sundays are the most difficult seats to get for a cancellation.
If you were looking to see the show during the week, there are always seats available at the box office the night of the show.
I say this from experience. I had just gone the evening of Oct. 11th I needed one more ticket for my sister and she just showed up at the box office 1/2 hour before performance and she was able to sit in right orchestra 4th row third seat in. She paid 111.00 for the ticket.
I know several people who have tried this on a Saturday & Sunday and they were not able to get a ticket. I was told by the person at the box office, Weekends are the most difficult tickets to get.
Good luck in your search!
Feel the Love - Les Mis