Well, there are several thoughts that come to mind.
1. mastermind groups with other CEO"s...sometimes being in "good company" with players of your calibre who are not in your industry, are a great source of input. they can play with you at your level because they're not afraid of you, and your level of disclosure is up to you.
2. trusted advisor - in the tradition of the motley fools who have permission to give his best advice to the king, no matter how unpleasant it may be, served the king's well. So cultivating that kind of relationship with someone outside the workplace is a great source. inside, it may be too risky since as you said, everyone has their own agenda
3. get an executive coach - not so much for their advice as for their inquiry. Their questions can help you discover your own solutions that are typically trapped within the circularity of your own thinking. They can reflect back to you things both positive and incongruent in your thinking process. Good ones will also challenge your positions, not because they think they know better, or have a better one but simply to help you escape the paradigm you're leading from. And, on the odd occasion, they may give you some advice with this caveat...that it's up to you to determine the validity and value of the advice and that you vet it with at least one other person. Lastly, they are your confidentiality space wherein you can explore thoughts, ideas and challenges without being judged. This is especially true of an external coach. Certified coaches have an ethics boundary about not sharing or acting on anything you talk about regardless of who is paying for the contract. They hold that boundary to the limits of the law,
4. a mentor, again, someone you can trust to not violate the vulnerability of the content of the conversation, someone whose attentive to your best interests and because they're not dependent on your approval will give you clean, clear opinions.