Imbued Silkweave Cover

Rank one is purchased from a vendor, but Rank 2 and Rank 3 are drops. Rank 2 drops off Broken Isle Furbolgs located only in Southern Val'Sharah, within the Steelclaw Vale. You can find it located just northeast of Smolderhide Thicket.. After completing the quest-line, the furbolgs are neutral but they can still be targeted and killed. It is definitely not a quick drop.

Below is a list I compiled of the 4 different cloaks and their possible secondary stats.

Imbued Silkweave Flourish…
of the Fireflash
114-229 Critical Strike
460-690 Haste
of the Peerless
114-229 Critical Strike
460-690 Mastery
of the Quickblade
114-229 Critical Strike
460-690 Versatility

Imbued Silkweave Shade…
of the Peerless
575-690 Critical Strike
114 Mastery
of the Feverflare
460-690 Haste
114-229 Mastery
of the Harmonious
460-690 Versatility
114-229 Mastery

Imbued Silkweave Drape…
of the Fireflash
460-690 Critical Strike
114-229 Haste
of the Feverflare
114-229 Haste
460-690 Mastery
of the Aurora
114-229 Haste
460-690 Versatility

Imbued Silkweave Cover…
of the Feverflare
460-690 Haste
114-229 Mastery
of the Harmonius
460-690 Versatility
114-229 Mastery
of the Peerless
575-690 Critical Strike
114 Mastery

Source: Battle.net

I don't know the results for this one yet, but each cloak can be made into only about 3 different combinations of secondary stats. Check the other cloaks for confirmed results.