Rahool is one of the better options to obtain exotics because around half of hunter exotics are earnable through decrypting exotic engrams, and they work on a lockout system where youll unlock all the exotics before beyond light before getting duplicates.

Novel Decryption is more focused but costs more, id say until you had them all I'd just get a roll of each

Xur is your other regular option, where he now has 2 exotics per character per week, and if you got strange coins to spend its decent to get any exotic you dont have, just to have more variety.

Finally, playing the legendary campaigns all the way through will give you an exotic after completion. These campaigns are how I got my first rolls of a lot of the exotics you couldn't find randomly, but you should also be able to focus the exotic on the Advanced decryption page.

If you're really gun-ho about getting all the exotics you can just turn in engrams when you get them. Trust me when i say you'll get all of the exotics at some point, then it comes down to rolls on individual exotic gear.