You can't. They were part of the old avatar system and are now retired.

Nor would it have been good to take them away from the people who spent a lot of sP to get them. There are plenty of current achievements, aim for those.

It would hardly be "right" for those of us who earned them to just have them yanked away, actually.

It's a reward for people for having been on Subeta for a while, actually :)

I enjoy having others see the Legacy achievements I earned. That's the point of having them.