Tons. I mean, hair texture and race aren't linked (just like skin color and race aren't), so it's not that rare. Plus, a lot of Blacks were able to pass, so many of these White folks with 4a/b hair have Black ancestry that they don't know about.
And I'm not knocking anyone who has a relaxer, but I find it interesting that most White folks who have 4a/b keep their hair that way (although, maybe they don't and I just don't know). Although, they probably don't grow up hearing that their hair type is unmanageable or that it needs to be fixed like us Black folks do. In fact, they probably get complimented a lot.