http://www.amazon.com/MADISON-MILL-27-Accordian-Porch/dp/B0009JEWBKBut Sorry, "Currently unavailable.
We don't know when or if this item will be back in stock."
70" is a fairly wide opening to span with one 'flimsy' gate.
The landlord needed a gate between dinning room (used to be a porch, it was glazed in to make a room) the span was 75" at the doorway. I built two 'posts' basically simple 2x4 stud frames 12 inches side to side and 38 inches high. I angled the joining ends, one can use a butt joint.
One side I attached a sheet of birch plywood, the top and the door opening facing end I placed a panel of same ply, then framed it in with pine corner molding. The other side I simply semi-framed the panel to where it would 'slip' on the rest of the structure, using tiny screws in pre-drilled holes. the holes were drilled with two bits, a wider bit (wider than the head of my screw) went halfway, the rest of the hole was drilled with a bit slightly larger than bit. The heads of the screws were thus deeper than 'flush' with the surface.
I secured the 'boxes' to the floor and doorway frame with lag bolts. 2 in the door frame, 2 in the floor. I slipped on the 'back' and screwed into place.
On those added structures I installed the 'pet gate'.
I finished the wood to match the existing dark stained door frame.
Other options is to think in the way of 'pedestals' where the box on either end is more square with a shelf on top that you can place potted plants or something.
It would probably be easier and look nicer to reduce the span of the doorway this way instead of trying to find a commercially built gate that would be able to span the distance.
BTW those wooded accordion gates need to be sealed for exterior used, their clear coat weathers off rather easily.