I know I'm resurrecting an old thread, which might be frowned upon, but I have news.
After never having seen a bottle of Zerex G48 in my life, I called NAPA and asked them if they could order it for me. The guy said of course he can get Zerex G05 and asked me how many bottles I want. Then I said G48, he said it doesn't exist, but he would be happy to check the computer. He checked, and two days later they had the two gallons I asked for. Apparently, any NAPA can order G48.
While it was a productive experiment, and I now have the coolant for my Volvo for a few dollars cheaper than the Volvo dealership wanted, it was exactly the same price that I payed at the BMW dealership for BMW coolant. They're all G48. So, with NAPA being someplace I tend to pass by daily, and the BMW dealership just slightly further and a bit more out of the way, it worked out okay. But if your local NAPA price is cheaper, this would probably be a pretty good deal.