See the FAQ: ISPs that provide Native IPv6 and IPv6 Transit Providers. One could possibly look at the BGP tables, that at least tells that at that point in time ISP x is using ISP y as a transit provider. But that doesn't tell much in terms of options that the ISPs have for getting IPv6 transit. It all boils down to willingness and cash. The latter is the biggest issue, as it will cost training and possibly hardware upgrades. The best ISPs can do, is do it gradually.

The issue is most common with the smaller ISPs. Broadband ISPs (especially the largest, such as VZ, Comcast, TWC, etc. that also serve business customers) have arrangements with IPv6-ready peers (such as Level3, which has arrangements with Comcast, and VZB, which peers VZ's broadband business). A further point about Comcast and IPv6: Comcast *as a business* is looking to deploy IPv6 across the entire company (from NOCs to customers); as such, they are already mandating support for IPv6 in new hardware. The United States government as a whole has already begun moving to IPv6 (per a GAO mandate requiring it back in the second Bush's first term). IPv6 will happen, even in the United States.