I have Vokun, Morokei, Nahkrinn, and Hevnoraak. Where are the the other..

Ahzidal -- acquired from the Dragon Priest Ahzidal, who can be found in the Nordic Ruin of Kolbjorn Barrow.

Dukaan -- acquired from the Dragon Priest Dukaan, who can be found in the Nordic Ruin of White Ridge Barrow.

Hevnoraak -- acquired from the Dragon Priest Hevnoraak, who can be found in the Nordic Ruin of Valthume.

Konahrik -- acquired after collecting all the previous masks. To collect this mask, entry into Bromjunaar Sanctuary is required.

Krosis -- acquired from the Dragon Priest Krosis, who can be found at the Dragon Lair Shearpoint.

Miraak -- acquired from Miraak at the conclusion of the main questline for Dragonborn.

Morokei -- acquired from the Dragon Priest Morokei, who can be found at the Nordic Ruin of Labyrinthian.

Nahkriin -- acquired from the Dragon Priest Nahkriin, who can be found in the Nordic Ruin of Skuldafn, during the main quest.

Otar -- acquired from the Dragon Priest Otar the Mad, who can be found in the Nordic Ruin of Ragnvald, north-northeast of Markarth.

Rahgot -- acquired from the Dragon Priest Rahgot, who can be found in the Nordic Ruin of Forelhost, south-east of Riften a top the near mountain.

Vokun -- acquired from the Dragon Priest Vokun, who can be found at the Nordic Ruin of High Gate Ruins, west of Dawnstar.

Volsung -- acquired from the Dragon Priest Volsung, who can be found at the Nordic Ruin of Volskygge, west of Solitude.

Wooden Mask -- acquired from within the central barrow in Labyrinthian.

Zahkriisos -- acquired from the Dragon Priest Zahkriisos, who can be found in the Nordic Ruin of Bloodskal Barrow.