As the commenter above said, you started to see them in the 1980s or maybe even 1970s but yeah they were called 'avacado pears' and were quite exotic. I was a teenager in the 80s and I never encountered an avocado, I don't think my parents would have had a clue what to do with one to be honest.
I've no idea when they became a fairly commonplace item. Probably the late 90s, early 2000s, from memory a lot of products that were previously considered exotic or extremely seasonal started becoming much more available around then.