When do tickets for individual games typically go on sale, ie a month prior, week prior, etc.?
About 2 weeks before kick-off. Clubs like Lech have to take into account European competitions, domestic cup etc., so some of the games are rescheduled, and that's probably why you can't buy tickets for them much in advance.
Were you trying to get Lech-Katowice or Lech-Legia tickets? The second game will, of course, be much more entertaining. ;)