BELFAST, Me. — Colburn Shoe Store, established in 1832, advertises itself as the oldest shoe store in the country. It has occupied the same small storefront on Belfast’s Main Street since 1905. It’s a place where the owner, Colby Horne , and his father, Brian , remember the brand and size their customers like, and those of their children, their partners and probably their siblings, too.

They know the shoe business. But they can no longer sell some of the most popular brands, like Nike and Adidas.

The Hornes are among a number of independent retailers who have been cut off in recent years by giant shoe manufacturers adjusting their retail strategies. In some cases, small businesses are required to make large yearly purchases of $20,000 or more. That outlay can amount to at least 500 pairs of shoes, far too many for a one-room shop to carry and sell in a year in addition to its other brands.

Independent shoe stores like Colburn have been Main Street mainstays, but others have been pushed out of business by competition from big-box stores and online shopping. Now, with some big shoe companies’ required minimum orders, the smaller owners are under more pressure.