To find out the procedures, guidelines, and information that already exists within an organization, you would go for the Organizational Process Assets. The role of the Organizational Process Assets is to implement policies and procedures that already exist with the company, implement process and guidelines for project management that already exist, and to keep file of historical information and experiences learned from the past. The policies, procedures, and guidelines are acquired from previous project management experience within the organization.

I agree with @Jbarbee that the organizational process assets should contain that information. Additionally, I think all these processes come from the previous experience of any project manager. Many take a template and populate or edit it in such a way that it better fits the company. However, in my experience, I have found most of these documents being made from various meetings between all the moving parts of the company. In these meetings, the team reviews each step of the documents in detail to assess their impact and their implications. This way there are more eyes on the document, which help refine it further.

I agree with the previous commenters as to answering the question of which group to go to find out various information about the company procedures, guidelines, policies, etc. The Organizational Process Assets (OPAs) are any assets related to the project available directly to the team and the entire company. This can include a wide array of information from any procedural-related assets to personal responses of other teams that worked on projects that can be related to the current one at hand. This information can be classified into two categories: processes and procedures and corporate knowledge base. Processes and procedures are any documents that have been filed and processed within the company. These documents may outline procedures, SOPs, or even policies of the company. Furthermore, the documents possess knowledge that can help the team maneuver through the red tape for projects and help them perform as efficiently as possible. Some previous lessons learned on similar projects may also be available to the team which can provide the team with insight into what works and may not work given a scenario in the project. On the other hand, corporate knowledge base refers to any intellectual property the company may have, "trade secrets", and sensitive data from previous test results which all could be beneficial for the team. These pieces of information are much more sensitive and attributed to the company's ethics, culture, and performance in the industry.

As mentioned in previous replies, organizational process assets (OPAs) are the primary source for procedures and guidelines that exist within a company. OPAs contain documented procedures and guidelines that provide a framework for how the work is performed in the company. Moreover, OPAs provide templates and forms that ensure consistency and save time during reporting and communication. Moreover, OPAs provide organizational policies and guidelines that look over different areas of the project such as quality management and risk management which ensures compliance with policies and external regulations/standards. 

As mentioned earlier replies, Organizational Process Assets (OPA) refer to the plans, processes, policies, procedures, and knowledge bases that are specific to an organization. OPA can come from various sources, such as templates of previous forms. This is one of the best ways to use standardized documents, as project teams can maintain consistency in their processes, reducing the likelihood of errors and misunderstandings. This approach saves time and effort in the planning, and based on that, this is one of the main parts of starting a project. This is a reliable way.

I personally choose the initiator or sponsor of the project and I know the reason for this in many personal and professional cases.
One of my most important experiences in PM work is that one should first know all the details and facilities and ease of hospital equipment specifically and check it thoroughly. The advantage of this work compared to other cases is that you check all the details yourself and solve the problems with your own abilities and creativity. And on the other hand, you don't spend time to review the past items and your time is saved to advance the project.