It's been a while but if I recall correctly, in order to unlock new Exotic armor you need to rank up to 16 with Rahool then you can scroll to the 4th page where you'll find it.

Bungie ruined the new exotic armour acquisition process when Final Shape launched. The way it works now is that you have to level Rahool all the way up to level 17 by decrypting prime and exotic engrams with him (which is a slow process if you're not rich enough to do the special decryption), and only after you do that and reset your rank can you unlock new exotics from him. Basically if you don't grind the game enough to get him to 17 before the new season starts and he resets, you will never in your life get any new exotic armour ever again. Thanks Bungie.

If you check on the Vex Invasion zones on Neomuna, every time you complete that event you are guaranteed an exotic you don't have. There are websites that will track when the events happen.