1940 to 60......and no the shade is not original......would have long ago worn out.
You can still get those milk glass diffusers.....so it may not be original....but does it matter?
Does it have a switch on the side that allows you tu turn on the center bulb or the side ones or all of them? does it take a 3 way bulb?

Yes, there are 2 switches. One that turns on the 3 candle bulbs and one that turns on the big one in the centre. (yes it's a tri-light) And when I say big.. I mean BIG. The bulb is shaped like a normal bulb, but it's way bigger.

As far as the milk glass goes... Based on the people who sold it to me, I'm going to assume it's orginal. They don't seem like the type of people who would have appreciated the lamp enough to buy a replacement shade. I think if it had broken, they'd have just replaced the lamp with something more contemporary.

Does the big bulb have a mogul base? may be hard to find.

Sounds like your large light in the middle is a mogul base. You can still get them, but they're getting harder to find. I can't see a switch on the bottom, so assume it does not have the night light. Many in that time-frame did, especially if it had that onyx insert on the base. It would have a small switch on the base. I agree with Linda this one looks forties up to mid fifties.

I don't know about the shade. So many of them were covered in a plastic film many people left on the shades to protect them from dust, it may be original, but most of the old ones had scorch marks where heat from the incandescent lights left their mark. I also suspect it may be a replacement somewhere down the line, albeit a retro one. The shallow-depth cylinder style (mid century modern) shade starts to become more common by mid-fifties, as opposed to the inverted vase-shape and is not so often seen in this more traditonally styled lamp.

You can get Mogul base 3-way bulbs online.
Casey

Here is a link that might be useful: bulbs

Yes, it's a mogul base... I found them at Home Depot. I might stock up on a bunch just incase they stop carrying them.

many garage lamps are found in places nearest to you yuo can reach through web rite

Ah, mogul base bulbs. I had almost forgotten about them. Incidentally, they do manufacture CFLs with mogul bases as well as an adapter that allows you to use a normal Edison bulb instead. They are easy to find through an internet search.