The last big map was for the 20th Anniversary in 2002.
As for the free ones, they have existed since the park first opened.
Dimensions have varied a little I think. The 1972 one was more of a vertical layout, with a squareish map. All of the more recent ones (Since Paramount Purchase) have been rectangular, I believe.
Themeparkbrochures.net has a decent amount of old maps/brochures.