There are some books online but your biggest difficulty is going to be finding audio sources. Dora Sakayan has released two books, relatively recently, called Eastern Armenian for the English Speaking World and Western Armenian for the English Speaking World. The books both come with audio CDs consisting of Dialogues and exercises. I have the Eastern Armenian book and CD, and I would recommend it if you are willing to shell out the cash.
Here is a link to the Eastern Armenian PDF. Not sure if the audio is available online though http://www.dss.am/images/menus/799/Arevelahayeren.pdf