They do this every away game for sales on a Sunday night, they'll be back on sale in the morning. I'd check just after 9am and they should be back online if you wanted to buy one
The PDF document is always wrong and has incorrect information. Our allocation Is 6000, should see a good 4000+ here http://mobile.seagulls.co.uk/news/article/milton-keynes-dons-tickets-on-sale-thursday-2958421.aspx