Hi there.  This is my first post so go easy on me!!

I've come by this Revo lantern and I can't find another example anywhere.  Can anybody help me with more information please?

Oh wow, that's seen better days 

Sorry I can't help directly, but I'm sure someone here will.

Welcome to the madhouse that is LG, by the way 

This looks like there is an upside down socket on the top middle without any ballast inside the fixture. I am not sure if it had a refractor or glass cover . Maybe a picture from the bottom up may help to see if a refractor was present.
Is there any other info about it that you know, like where was it found?

Is this enough for you?

from the top as well.

Is this enough for you?

have you tried to remove the screws holding this cover on?
the hole in the centre is there a socket or anything in it or is it open to the inside?
I would assume there is "nothing" at the opening and there WAS a gland that sticks down and there would be a assembly with the lamp holder AND glass shade as it LOOKS like a GAS lantern converted to electric / a GAS lantern style for early electric era
I assume you and this is in the UK somewhere

By checking the insides you may know what it was (gas or electric) based on the components.

found a pic online and it looks like an incandescent bulb was bare hanging down from the hole in the top
I posted a link in the main gallery pic of this fixture
http://www.streetlightonline.co.uk/77b.htm

This is a very rare Revo 'Spondon' lantern for 100w-200w GLS lamps, made around the 1920's to 1930's. As a rule of thumb usually anything made of Cast Iron is pre WWII and Cast Aluminium is post WWII. It would have always been an electric lantern, and the lamp would just simply be bare, as many lanterns of the period were. Look closer at the lamp holder, as two versions of the same lamp holder were offered. The first would simply screw to a threaded rod, however the second would suspend via a series of springs as an 'anti-vibration' mechanism to prevent the fragile filament from snapping prematurely. Typically the latter would have been more expensive from factory, so as such is far more rarer. This is such a good find in this day and age, make sure to keep it stored in a shed at least to prevent it degrading any further.

There's three screws that hold the reflector to the canopy, and will no doubt be seized in so you'll need to heat the area to remove them. If you do attempt this, don't just focus on the immediate area around the screw, as you'll snap the Cast Iron through thermal shock. You need to gently heat the whole piece of metal before you focus on the area around the screw, this'll stop the cast iron cracking. The reason I say area around the screw is because you only want the metal to expand to break the seal, if you heat the screw with it, both expand and you won't actually get anywhere. Upon attempting to turn the screws free, tighten just slightly first, and then wriggle back and forth until you feel the screw begin to turn. You'll know if the screw is turning or snapping because you'll feel/hear a slight grinding or rough sensation through the screwdriver if the whole screw is free. If its just the head turning, you'll feel nothing. This applies to every screw on every lantern you come across. If you feel nothing, you may need to heat the area further, or give the head of the screw a tap with a hammer to further help break the seal. Don't use WD40, as all this is is a water displacer, not a lubricant. A fine oil should more than suffice for the job.