How much impact on sales volume does being an award winner (such as a the Whitney awards) make?
Is there a place to find out how many books a certain author sells? Or publisher?
The answer to the first question is "I don't know" because the answer to the second question is "No."
Most publishers do not give good information on their sales. They might tell you that a particular book has sold over X number of copies, but that's about it. Or they might claim a book is a best-seller, which could mean that it's hit an unspecified sales level or that it's simply sold more copies than the other books they publish. No one knows.
An author might be willing to give specifics on sales if they're having a one-on-one conversation with you, but there's no way to check the accuracy of those numbers. Also, their numbers will run anywhere from three months to a full year behind, depending on how their publisher pays royalties.
As far as awards boosting sales, in general, an award will have a positive influence on sales. All things being equal, a customer tends to believe that if a book got an award, it must be good. Obviously, a Newbery is going to really boost sales. A Whitney, not as much, due to market size.
Any Whitney winners want to comment on how they feel the award impacted their book sales?