I had this problem last year, too, since the calendars were sold out when we went to the park in November. This year I bought the 2013 calendar on the Disney Wonder last August to be sure they wouldn't sell out before our trip last month.
I can't locate the Disneyland calendar online at the Disney Store. I could find the Disney World calendar at the Laughing Place at http://www.laughingplacestore.com/Category-RC-116.asp. Hopefully someone will post a phone number you can call; I can't remember what it is--sorry!
The calendar sells out ridiculously early. We were there in August 2011 and again in November 2011. I did not see the calendar during my August visit, but apparently it came out sometime between those dates and was sold out by our November arrival. I was disappointed.
This year I bought my calendar during our end of July visit. I would be surprised if there are still copies around the parks. To find out though, call Disneyland DelivEars at 800-362-4533. I hope there's still a calendar available for you.
ETA: I saw one listing for it on eBay. It is being offered at a much higher price, of course, so I don't know if it is that important to you to have it. HTH.
I ordered one last month. I called the merchandise number on the bottom of an old World of Disney store receipt. It was about $11 plus tax, and about $7 to ship, if I remember correctly. Make sure they know you want Disneyland, not Disneyworld.
The number was 1-877-560-6477
By the way, it is a 16 month calendar, so you can start using it right away!
I just picked one up for a friend at the little sundries shop in DLH at the counter - not the larger gift shop. But I'm not sure if they ship from there.