Contact the company HR dept and ask what temp agencies they use and for what type of temp. Some larger national companies with state or local divisions may have HR departments at each level. Some have contracts with specific temp agencies for specific types of temps like IT, nursing, admin, janitorial, accounting, etc. Ask the questions.

Food for thought: It can be an extremely difficult and lengthy process to simply fire an employee, especially for large companies. For this reason, some companies will hire exclusively from temp agencies. If a worker isn't working out, just call the agency and ask them to send a different person in the morning. No HR fuss!