yea check with the manager of the store. On some the store owns the land and on some they rent the land from the developer (especially in a shopping center). So the manager would know if the landscaping is his job to hire out locally, or if the regional manager does a master contract for all the stores in thier region, or if the developer provides the maintenance as a part of the lease.
The manager should be able to give you the developer or property managers contact info. if the landscape is provided by the developer/ management co and the manager does not give you the info -look fora vacant space in the center, it will have their number or the number of a realtor/broker who could steer you in the right direction.
hope that helps