How to Find Peer-Reviewers Who Aren't Busy (During the Summer)
You're not being asked to find reviewers who are willing to review your paper. You're only being asked to suggest reviewers. There is no guarantee that any of the reviewers you suggest will actually be the one(s) who review your paper.

Therefore you should not so much identify people who have time as you should identify people who can review your paper. If you're still concerned you could identify people other than the superstars, but suggesting superstars is fine, because the superstars probably know others who can review your paper (so they can suggest someone).