Board Thread:Questions and Answers Forum/@comment-26322332-20150618130110/@comment-24057866-20150618140801

They were removed a month prior to the House of Wolves launch, probably to make room for the Prowling Wolves events. From the April 16, 2015 Bungie Weekly Update:

Players have reported that they are unable to find Blades of Crota on Moon Patrols. If you’re still looking for the Blades of Crota, you can still find them in the Fist of Crota mission.

I don't think they're coming back.