All major Linux distributions provide some way of package installation and updating, using mirror sites.
Some of those archive mirrors are reachable via IPv6, some not. But there is no clear indication as to which one is and which isn't.
Instead of maintaining a static list of IPv6 enabled archive mirrors, I've created some scripts that parse the official archive mirror list of a Linux distribution, and 'enhance' it with IPv6 information:
Official archive mirror list
Same list page with IPv6 information
The new pages have a link to the PHP source code.