As the previous poster said, tickets went on sale in July. The Parks Blog tends to make the announcement a few days before the advance sale. The first weekend in October tends to coincides with Gay Days, so that Friday night party is usually one of the earlier ones to sell out, while the weekday parties (e.g., Tue) tend to take longer to sell out (assuming things follow the same pattern).
2017: Tickets went on sale to DLR Annual Passholders, DVC, and Disney Rewards Visa Card Holders (phone only) on Monday, July 17 and to the general public on Monday, July 24.
2016: Tickets went on sale to DLR Annual Passholders, DVC, and Disney Rewards Visa Card holders on Thursday, July 21 and to the general public on Thursday, July 28.
2015: Tickets went on sale to DLR Annual Passholders, DVC, and Disney Rewards Visa Card holders on Wednesday, July 22 and to the general public on Wednesday, July 29.