What a dumb policy. What could be gained from not disclosing a source? Seems like you'd want to help out a company that is making things for you to sell.
You don't expect the people who sold you your bike frame to tell you what factory made it. You don't expect Levi-Strauss to tell you who made your blue jeans. You don't expect the people who sold you your computer to tell you made it. Why should they? It's standard practice in nearly every industry not to reveal product sourcing information. It's an open secret in some cases, but they're still not going to tell you.