You can shard using Alfresco Community Edition. The only thing not supported is the dynamic shard registry, so you need to manually adapt the Repository-tier list of available shards / URLs.
Though to be fair, it should be straightforward to implement the dynamic shard registry feature for Community Edition as well - the API is defined in the public core and SOLR itself is "edition-unaware". You'd only need to register the bean and manage the data storage (via AttributeService). It is one of those features that are so simple, it is unclear why Alfresco chose them to be Enterprise-only (like the "live configuration change on subsystems" one).
