Haha yes they have always existed, even the mighty T Rex consumed BCAA's each time he had a kill, how do you think he got so massive??
If you are talking as a supplement, I know they were around on the 80's, Weider used to market BCAA and AAE tablets, not sure about powders, but definitely tablets as processed BCAA's taste like shit a tablet was probably the easiest way to get the down.
I like my BCAA's in the form of a nice t-bone or rack of ribs these days.