Where is the expanded seating?

I learnt about this mod somewhere around a20, and when 1.0 released I was messing about in creative mode with a friend. We were adding this mod to the vehicles we spawned. Now we're at 1.4, I've increased my playtime by about 100 hours, most of my games have got to at least day 35, and I still haven't found this mod or schematic!

Where tf is this mod!?