Here are all the sets sold by Cyrodiil town merchants. These were found on the PC version.

Originally submitted on  Reddit by powerman123 and related to [PC]. Map added.

Patch 2.7.x altered the offerings of the vendors (sets with a * will be removed) and reduced their prices (75%).

Bruma (Medium)

  • Eagle Eye 12,000AP
  • Hawk’s Eye 12,000AP
  • Kyne’s Kiss 12,000AP
  • Sentry 12,000AP
  • Shadow Walker 12,000AP
  • Shield of the Valiant 12,000AP
  • The Morag Tong 12,000AP
  • Vengeance Leech 12,000AP
  • Ward of Cyrodiil 12,000AP

Cropsford (Light)

  • Almalexia’s Mercy 12,000AP
  • Buffer of the Swift 12,000AP
  • Curse Eater 12,000AP
  • Desert Rose 12,000AP
  • Grace of the Ancients 12,000AP
  • Light of Cyrodiil 12,000AP
  • Robes of Alteration Mastery 12,000AP
  • The Arch-Mage 12,000AP
  • Wrath of the Imperium 12,000AP

Vlastarus (Heavy)

  • Affliction Item 12,000AP
  • Alessian Order 12,000AP
  • Bastion of the Heartland 12,000AP
  • Beckoning Steel 12,000AP
  • Blessing of the Potentates 12,000AP
  • Crest of Cyrodiil 12,000AP
  • Deadly Strike 12,000AP
  • Elf Bane 12,000AP
  • Ravager 12,000AP
  • The Juggernaut 12,000AP

Regional Equipment Vendor

  • Unknown Alik’r Desert Item 5,000AP
  • Unknown Auridon Item 5,000AP
  • Unknown Bangkorai Item 5,000AP
  • Unknown Coldharbour Item 5,000AP
  • Unknown Craglorn Item 5,000AP
  • Unknown Deshaan Item 5,000AP
  • Unknown Eastmarch Item 5,000AP
  • Unknown Glenumbra Item 5,000AP
  • Unknown Grahtwood Item 5,000AP
  • Unknown Greenshade Item 5,000AP
  • Unknown Malabal Tor Item 5,000AP
  • Unknown Reaper’s March Item 5,000AP
  • Unkown Rift Item 5,000AP
  • Unknown Rivenspire Item 5,000AP
  • Unknown Shadowfen Item 5,000AP
  • Unknown Stonefalls Item 5,000AP
  • Unknown Stormhaven Item 5,000AP
Notes: 
Items sold are of purple quality

Each set has its own box. The contents of the boxes are random but it will be a piece for the set you choose 

Golden Vendor

A special vendor that only appears on the weekend.

There is a special page *updated every weekend* for the vendor here .