Here's a quick list of some known firewalls that support ipv6. I'm sure their others, but these are just a list that I'm aware of.
Fortigate ( linux based )
pfsense ( bsd based )
Halon SR ( bsd based )
linux iptables with ipv6 ( kernel 2.6.x )
cisco ASA ( linux based )
Juniper ( bsd based )
PaloAlto ( ????? based )
Cyberoam ( linux based )
Checkpoint ( linux based )
( note: I've have worked on all of the above platforms ( bold ) with regards to ipv6 and they don't always support dynamic routing for IPv6, and might lack RIP-ng or OSPFv3 , they also might be very restrictive , base on software such as support for DHCPv6 server )
With the big push for IPv6 ready gear and IPv6 migrations, the vendors are slowly catching up and moving forward.
Freelance Security and Network Engineer
kfelix "at_symbol"hyperfeed dot com