The American First Day Cover Society is producing the Official Boston
2026 World Expo show covers, both serviced and unserviced. The press release is many places. You can see and order all 8 cachets here. They will also be on-sale at the AFDCS' stand at the show, booths 18, 19 and 20 in the Americas Pavilion. Also there will be cachet designer Chris Calle, who has shown willingness in the past to provide autographs.
Prefer to order by mail? Send orders (payable to AFDCS) to AFDCS Sales, Box 44, Annapolis Junction, MD 20701-0044. However, covers will be sent after June 1.