We are digging up all sorts of great images on the Smithsonian’s site. Here’s one near Center Market with a view of the Old Post Office Pavilion in the background.
View of the Center Market of Washington, D.C. from the north entrance of the United States National Museum, now the National Museum of Natural History, on October 16, 1909. There are horse-drawn carriages and carts, vendors, storefronts, and the Old Post Office is in background, center. In the foreground is the large wooden gate to the grounds of the Natural History Building and a small guard house next to it