How common are they?

Two old farm items.

One.....what we called an elevator.....drag  chain with cross pieces.......used to put ear corn into a crib and small square hay bales into a barn loft. Brands can remember were Kewaunee, Owatonna, John Deere? Maybe others? Any good working models remaining?

Second: Wire frame corn cribs. Look like a grain bin, but sides made of wire. Used to store ear corn.

Still out there? 

We had a Deere elevator when I was a kid.  When it wore out and rotted out we got a New Idea.  I almost died on that New Idea, no exaggeration, but that's a different story.  We bought a longer one, at the time Mighty Handy had bought out New Idea.  I'm not sure, this was probably about 20 years ago.

This fall, I was too efficient.  I like to take it down and park it away from the barn when we're done with hay, because it's sort of in the way for cleaning the pens, and water can collect in the bottom of it and rust.  Typically don't get around to it for a while.  This year, I was on the ball and took it down to the area it gets parked in the off season.  Huge wind storm came through and knocked a tree down on it and wrecked 2 or 3 sections.  Dealer said Mighty Handy doesn't make them anymore, just no demand.  He also told me that when word got out that they weren't making them, an Iodine mine in Oklahoma (I think) came to the factory and bought everything they had because they used them.  

So. . . if anyone has a New Idea or Mighty Handy elevator around, I sure could use a couple sections!!!

I'm in Michigan.  How long is your elevator?

Okay, so... the reason for running a silage elevator, rather than a blower, was about PTO horsepower at a given speed.

My Grandfather ran a silage blower off his WC, and later, off his D17.  For a little while, When I was very young, He HAD an earlier JD twin (I THINK it might've been a G) which I think he wound up with as result of a neighbor/friend passing away.

I asked him many years later about it, and his explanation was to the effect that, in a macro sense, it was good at a few things, but from a performance aspect, was very weak in others.  The one thing he specifically noted, was that the 2-cylinder engine could not run a blower hard enough to fill a high silo lift, but the WC 'could do it all day'.  I suspect it had to do with governed RPM, belt pulley diameters, and HP/HRs/Gallon at full governed speed.  Note that A blower, wether loaded with silage or not, draws a considerable amount of input horsepower because it's moving air through a rather lossy tube.

If this actually WAS the case (and I don't have any way to test/prove either way, but would bring my WD to try it), then it would stand to reason why one would opt for an elevator instead... and JD would likely have been very committed to getting mechanical elevators out to deal with that situation.

An elevator, in comparison to a blower, is probably going to come out much more energy-efficient for loading the silo, but it certainly won't be as fast, and it will require considerably more maintenance to keep it operational.  The popularity of blowers for silage is very significantly on SPEED... because, unlike what most non-agriculturistic people generalize, farming is NOT a leisurely paced occupation.