I never figured these exact wheels did exist. I was looking for something similar. Many companies that make OEM wheels also have similar models of their own. It really wouldn't surprise me for someone to come out with an upsized clone of the factory wheels. That what I'm looking for.
I bought some American Racing wheels for my Yukon XL that were the same as what the dealer was selling, but half the price. Both were mad by AR, the only difference is that they didn't have the GMC logo in the center - they had the AR one instead.