Here’s an episode of “Antiques Roadshow” that fans of the WGBH series won’t want to miss. At a taping in New York City on Aug. 9, a “Roadshow’’ guest entered the Javits Convention Center with a stunning trove of old-time baseball stuff inherited from her great-great-grandmother, who’d run a boarding house in Boston in the early 1870s. The memorabilia includes extremely rare baseball cards of members of the Boston Red Stockings and a letter written by several team members to the owner of the boarding house. Three of the most famous names in early baseball — Harry Wright, his younger brother George Wright, and Al Spalding — were just a few of those who added their words to the letter. Imagine the owner’s surprise when the collection was appraised by sports memorabilia specialist Leila Dunbar at a cool $1 million. “This is the largest sports memorabilia find in the 19-year history of the series,” Marsha Bemko, executive producer of “Antiques Roadshow,” said Tuesday in a statement. No word yet on when the Red Stockings episode will air, but we hear it will be one of three New York-based segments slated for 2015. Can’t wait.