In my experience, Source Control refers to a process which ensures that Suppliers meet a set of procurement quality, cost and schedule performance standards. Suppliers hoping to meet these, and perhaps additional standards imposed by the procuding business or agency, must have their internal control processes and performance assessed, and if they meet the standards, they are included on an approved Supplier List for future procurements. To stay on the list, they must continue to perform to acceptable quality, cost and schedule standards, and pass periodic re-assessments.
Change Management is a much broader topic related to the establishment of technical, cost, schedule, risk, Supplier and perhaps other baselines. and the subsequent formal evaluation and approval by the project stakeholders of proposed changes to those baselines.