Hello David,
This snort rule is available in the latest update (18th August 2016) of SRU release which is Sourcefire Rule Update 2016-08-17-003 .You can download it from the following link.
https://software.cisco.com/download/release.html?mdfid=286259687&softwareid=286271056&release=Rules%20Updates&relind=AVAILABLE&rellifecycle=&reltype=latest
Please navigate to Rule updates and download the rule update using your credentials.
Rate and mark correct if the post helps you
Regards
Jetsy