We have a mailinglist we use for various co-ordination efforts. It is very low volume as we prefer to spend time auditing code, rather than talking about it. This is also the reason no names appear on the audit results page. We are interested in better code, not bragging rights.
To join the list, send an empty message to audit-subscribe@mongers.org.
Post your messages to audit@mongers.org.
Browse the archive (online December 2017 -- maybe), and either contact the person working on an application you are motivated to audit, or post a notice stating you are starting an audit.