So how should I go about getting Meek Pluggable Transports and bridges with IPv6 addresses?
It really strange, but I guess BridgeDB doesn't give bridges with meek transports anymore. Neither on their website or on their mail.
You still have a lot of other pluggable transports such as fte, obfs3, obfs4(usually the way to go) and scramblesuit. You can get them all with IPv6 addresses. You should try to use one of them.