Openfire Clustering in an Loadbalanced Environment

We want to setup an Clusterd openfire (3.6.4) Solution.

We have 2 frontend multipurpose (with openfire) servers, and 2 backend (mysql) servers.

I understand that the available cluster plugin only works with an (unfindable) outdated version of Coherence.

Is there someone who can provide this version of Coherence?

Or should I take a look at the jboss (not well documented) way of clustering?