Including (almost) everyone

What you need is information and insight from individuals who can actively contribute, are engaged, are ideally open to change (or at least would like to see things change for the better) and understand and agree to the aforementioned rules. These engaged contributors should come from all parts of the business—if they are involved in product creation and delivery, they should be considered. You will need a broad set of information and data to move forward, therefore you need to get a broad set of engaged contributors involved.

To ensure you can identify as many people as possible, you will need to establish a good network across the organization or at the very least access to those who already have one—especially if your organization is sizable as it's not practical to identify and be on speaking terms with everyone. You will normally find that individuals who have been around for a good while normally have a well-formed and mature internal network you can tap into.

You should proactively engage with these individuals and explain what you're trying to do—remember the aforementioned positively worded goals and rules of engagement—and ask them to help build up your list. If you can also add them to the engaged contributors list then that will speed things up as they can do some of the evangelizing and leg work for you. 

As you start compiling the list of participants—which for a large organization can be quite daunting, demanding and not without effort on your part—you will no doubt find that there will be some degree of natural selection as you start to ask people to contribute; some may say they're too busy, some won't want to be involved for reasons they don't want to disclose, some may simply not care enough either way.