I would assume even most minor leaguers have a contract to use one company’s gloves/bats/shoes, etc.
Low level minor leaguers don’t make a lot of money for the most part, so the team’s will try to get them the best stuff they can afford. But even a Rookie League fielder is going to have a much nicer glove than the rest of us can find at our local sporting goods store.
Players may start off with some of their own gear like shoes and some shirts, but the teams will supply the rest.