You can buy discount Disneyland tickets at Costco, Safeway and Disneyland Good Neighbor Hotels in Anaheim, California. You can also receive discount tickets through authorized online sources like Park Savers.
When seeking discounted Disneyland admission, never buy partially used Disneyland passes. Disney tickets are non-transferable, which means they are only legally usable by their original purchasers. If you get to Disneyland's entry gate with a used ticket that doesn't work, you won't have any recourse but to buy a new ticket at full price. Never buy Disney passes on eBay or Craigslist, which see their share of scammers selling worthless Disneyland tickets.