1. Online Directories: Check online business directories and platforms like Alibaba, ThomasNet, or Yellow Pages. These platforms often list manufacturers along with their contact information and details about the services they offer.

2. Industry Associations: Explore industry associations related to printing and graphic arts. These associations may have directories or can provide recommendations for reputable offset printing manufacturers. Examples include Printing Industries of America (PIA) or regional printing associations.

3. Trade Shows and Exhibitions: Attend printing industry trade shows and exhibitions. These events often feature various manufacturers showcasing their products and services. It's an excellent opportunity to meet potential suppliers and learn more about their capabilities.

4. Networking: Connect with professionals in the printing industry through social media platforms like LinkedIn. Join relevant groups or forums where you can ask for recommendations or insights about reliable offset printing manufacturers.

5. Local Printers: Contact local printing companies and ask for recommendations. They may be willing to share information about their suppliers or point you in the right direction.

6. Online Searches: Conduct specific online searches using keywords like "offset printing manufacturers," "commercial printing companies," or similar phrases. Explore the websites of companies that appear in the search results to learn more about their services and capabilities.

Remember to verify the reputation and credentials of any manufacturer you consider working with. Reading customer reviews and checking for certifications can provide insights into the quality of their services. Additionally, inquire about their equipment, production capabilities, and any specific requirements you may have for your printing projects.