Make sure you are patched to at least Skyrim patch 1.6 in order for the quest markers to appear.

You can find an Assassins Bow in the quest loot which has a unique enchantment that will help you get all of the hearts and flesh needed. Many of the armors require human parts to craft. There are a total of 10 forge spells, each armor set is craftable according to its color variant per spell. Locate the 5 assassin grave sites, exhume the shallow grave mounds, and loot the corpses to gain access to the spell tomes that will teach you the forging spells. To craft this gear you should have received an initial quest marker (look in the Miscellaneous section of your quest journal). The second chapter for this set is still coming soon according to the developer. Black Sacrament Armor is a standalone, fully modular and customizable armor system comprised of multiple parts, add-ons and color variants, as well as a handful of new weapons. The Black Sacrament Armor pack is the first installment of The Black Phoenix Stealth Assassin guild mod. First up let’s look at the Black Sacrament set. The creator of the two sets is AmethystDeceiver and I think they really have out done themselves with their Black Sacrament and Lustmord Vampire armor mods. Since getting back into Skyrim I’ve been looking at the mods out there again and I found two light armor mods that I think are amazing looking! Both armor sets are available from Skyrim Nexus Mods and the best way to install each is through their mod manager.

Skyrim leather armor mods