The Oakland A's announced today that they will place tickets for possible games for the postseason on sale to the general public starting Tuesday, September 17th at 10 AM PDT.
Drawback is that you get a ticket to a specific games, such as Game #2 in the first round, but not a specific date and/or time the game starts. But if you are going in the Bay area the first half of October, you might get a ticket at a decent price, but you should plan to buy right at 10 AM on Tuesday.
The LA Dodgers have not yet announced when it will place its tickets on sale to the general public.
And the other California teams (Angels, Padres and Giants) have no real chance of going to the post season in 2013.
By the way, here are the mostly likely dates for the A's playing, and they will more than likely play the Detroit Tigers, not sure who will be #2 and who will be #3, it is close with weeks left in the season.
Game 1 AL Division Winner #3 @ AL Division Winner #2 Fri, Oct 4
Game 2 AL Division Winner #3 @ AL Division Winner #2 Sat, Oct 5
Game 3 AL Division Winner #2 @ AL Division Winner #3 Mon, Oct 7
Game 4* AL Division Winner #2 @ AL Division Winner #3 Tue, Oct 8
Game 5* AL Division Winner #3 @ AL Division Winner #2 Thu, Oct 10
Also it is the best 3 out 5, so games 4 and 5 might not be played (You would get a refund for the ticket purchased, if bought directly from the team). Also rain can cause games to be delayed and move the schedule around.