You are asking a good question which is not easy to answer.
A list of IPv6 certified products (hard- and software) can be found at www.ipv6ready.org
if a vendor’s product does not appear on this list, it does not mean it doesn’t support IPv6, because registration is optional.
An organization working on their IPv6 strategy will have to assess the whole network at some point, based on the requirements for IPv6 which are derived from the IPv6 strategy (what RFCs need to be supported). This assessment is labour intensive, but it can be done by consultants.
Hope this helps