Everything I have seen says the entire base set has a white parallel. They were inserted at 1:6 packs so 4 per box. I went through multiple sell sheets, BCP, etc. and all are saying the same. The problem, supposedly, is tha tthe white is hard to actually see. When you have one in hand it washes out some of the other colors, almost like having to hold a baseb and a parallel next to each other to compare.
Didn't find much on eBay, but did here
https://www.collectors.com/search/all?searchterm=2006%20bowman%20heritage%20white
My sins have come to face me, I can feel it
That I have lived my life in vain
And now I know I'll reap the seeds I've sown