There are two ways that DNS based IP address blacklists can support IPv6;
Below the latter;
There are a lot of combineed RBL test sites. AFAIK this one is the only one
which accepts IPv6 input;
MultiRBL.valli.org - Blacklist, Whitelist and FCrDNS check tool
They also have a blacklist list;
MultiRBL.valli.org - Informations about all RBLs
There are some additional IPv6 capable RBLs in this list.