I've been lurking here for awhile, so I thought that I would try to contribute a little bit by passing along some resources I have found in my neighborhood (Near north side of Chicago).
Sam's Wine and Spirits near the intersection of Clyborne, Sheffield and Willow (behind Goose Island Brewpub
), has a small gourmet food market in the back corner called the Marcy Street Market. They sell four different brands of canned Italian tomatoes, dozens of olive oils, Many varieties of olives (in jars and from an olive bar), excellent sliced to order pepperoni (and other cured meats), a wide variety of cheeses (including Mozzarella di Bufala) and a number of other ingredients that would feel perfectly at home atop a pizza. Plus they have thousands of different wines and hundreds of different beers to choose from. They have 2 suburban locations, but I haven't visited them so I don't know if they also have gourmet food markets.
The Dominick's grocery store at the corner of Clyborne and Division stocks 6 in 1 ground tomatoes and Harvest Gold flour. They usually only have three or four cans of the tomatoes on a bottom corner shelf, but hopefully if the demand increases they will increase their stock. This is the only Dominick's where I have found these products, but they may also be available at other locations.
The Spice House (founded by Bill Penzey Sr. and now owned by his daughter and son-in-law) on Wells Street just south of North Ave about a half block south of Second City has just about any herb or spice you can think of, and of much better quality that can be found in a grocery store. They also have locations in Evanston on Central Ave and in Milwaukee. I would assume they have the same selection at all three shops, but I have not been to the other locations. They also sell mail order.