This submission is from Deadeyé! A lot of the pieces of this set is BoE, so you could get a good head-start by searching the auction house (check to see if a friendly blacksmith has the helm pattern). Other pieces come from a bunch of different raids and instances, but nothing beyond early WotLK content so just get a small group together for help and start hunting!
This set comes from Foxfyr of Eitrigg <Victorious Secret>! The Darkmantle pieces can be obtained in the dark moon fair and while time consuming can be obtained solo. The axe drops off Al’ar from Tempest Keep, so bring a friend, while a group of friends will most likely have to help you grab the dagger in 25man Ulduar. Finally, the helm drops off Illidan in the Black Temple, which will also require a couple of friends at least.