Easiest place is the Welcome Home Wednesdays gatherings at the BoardWalk or the
DVC presentations on a
Disney Cruise. All attendees usually get something small like a DVC baseball cap or a window sticker.
Disney Cruise Line gives all members a package in their stateroom with things like lanyards, plastic pen, DVC magnets on stateroom doors.
The larger items (beach bags, towels, etc.) are given away via random drawing at the events noted above. You need to be lucky more than anything.
Some DVC merchandise is available for sale in resort gift shops.