Acolyte's Guise
Quest reward from The Better Part of Valor. There are 8 items currently in Wowhead that modify the Necrotic Acolyte disguise, either from the campaign's extra action button or the toy.
The 
Acolyte's Guise is a toy obtained from the quest 'The Better Part of Valor' during the Shadowlands campaign in Maldraxxus.
Guide awaiting review
Complete the Shadowlands Campaign
Progress through the Maldraxxus Shadowlands campaign to reach and complete 'The Better Part of Valor', which rewards the Acolyte's Guise toy. Several disguise modification items, such as the 
Discarded Grimoire, 
Sorcerer's Blade, and 
Amethystine Dye, are very likely to be picked up naturally as quest rewards while completing the campaign.
Customize at Moret the Vogue
Visit the mannequin next to Moret the Vogue in the south-eastern part of the House of Rituals at 71.6, 33 in Maldraxxus to modify your Necrotic Acolyte disguise options. There are 8 items in total that can alter the disguise, though only 7 are included in the Crypt Couture collection.
Obtain the Ritualist's Mantle
The 
Ritualist's Mantle is a group quest reward that can be skipped or may be dropped if you leave the area before completing it, so attempt to complete it while you are in the zone.
Farm Mucosal Pigment from Slimes
The 
Mucosal Pigment drops from slimes or slime giants in Maldraxxus and is likely only available after completing the campaign. The House of Plagues area is a smart farming spot for this drop.
Get Jagged Bonesaw from Collector Kas
The 
Jagged Bonesaw is a confirmed drop from Collector Kas in Maldraxxus.
Farm Green Disguise from Congealed Plague
Killing Congealed Plague in Maldraxxus can drop an item that changes your disguise to the green color associated with House of Plagues acolytes.
Tips
When used inside Maldraxxus the toy has a 30-minute cooldown, while using it outside Maldraxxus increases the cooldown to 1 hour.
The toy's disguise duration is approximately 23 minutes, though completing the Crypt Couture collection may extend it to 30 minutes.
Use the disguise modification items before leaving the relevant areas — using them before receiving the toy itself does not appear to lock you out of the options.
