1. Firstly you should complete quest chains of your professions
You can see them here http://forum.epicwow.com/topic/23838-tsepochki-kvestov-professiy-legion-aktualen/
2. Level your professional skill up to 800.(If you have already done it before, there is nothing wrong)
3. Complete the quest http://wowhead.com/quest=46774/разрушитель-пустоты of http://wowhead.com/npc=120183 on the Broken Shore
4. Learn legendary item recipe for 212 gold and 20 silver coins in Dalaran
5. Return to the Broken Shore to http://wowhead.com/npc=120183/командир-чеймберс and buy http://wowhead.com/item=147451 for 800 http://wowhead.com/currency=1342 Attention! You will be able to buy http://wowhead.com/item=147451/ every Wednesday to Friday(The building exists for 3 days)
6. Complete http://wowhead.com/item=147451 at http://wowhead.com/npc=120221
7. Than start a quest chain for a legendary item (There may be several quest chains for 2 legendary items):
(Today only several quest chains have been realized, they will be listed below)
http://www.wowhead.com/spell=239413/the-sentinels-eternal-refuge
http://wowhead.com/spell=239414
http://wowhead.com/spell=239415
http://wowhead.com/spell=239412
Thanks for @Justicar translated!