I just picked this up this morning. At first glance I thought it was just some cheap knife. But the hangers on the scabbard peaked my interest. Since I could see an identifiable mark on the blade I thought for .50 cents how can I go wrong.
So Is this an authentic 1918 AU Lion, Mark 1, Trench Knife ? Obviously its missing the handle.
My little bit of research makes me wonder if the tang has been cut down it measures 4.050" long.
So if this is authentic, What is the value as it sits now? What are my chances of finding just a handle for sale?
Or should I just spend 30 to 50 bucks on a reproduction one and use the handle off of it?
And just for the record, I would never try to pass this off as 100% authentic. As a mater of fact Im sure Id never sell it.
Id just add it to the collction of my other rusty old knives.  
Any help would be great.

I don't think there is a hope in hell of finding a original grip, cross guard and locking bolt unless you buy one with a fubar blade. I would go with a repro instead. I gave $50 for my current one, but they sell for much more.

Nice original scabbard, blade and pommel nut.  As for finding a handle in the wild,  doubt it would ever happen.  If it were me I'd leave it as is since the repro handles currently available are so poor in appearance they do not even come close to what the real handle looks like.  

I'd have bought it too as it would be the closest I'll ever get to an Au Lion trench knife.  Even in it's current state it'd look good next to my LF&C M1918 MkI.

There's a fair chance that you have a Mark One Au Lion that some WWII soldier modified.
The Mark One in both American and Au Lion versions were heavily issued early in the war to paratroopers and Rangers, until the supply was exhausted.
It was common for them to modify and customize these knives.
As such, it would have more value as a collectable then if fitted with one of the current, really, really, horrible Chinese replica handles.

The current replicas are so terribly bad such a handle would probably detract from any value.
The Japanese replicas of the 60's and 70's would be much better if you can find one, but I wouldn't use a current handle.

Original WWI Au Lion knife, and a cheesy current Chinese "replica".
Note how the Chinese isn't even remotely like an American or French original, or a Japanese replica:

I'd find somebody to sand cast one from an original.

For now I've made a new grip out of stacked polycarbonate. It'll do till I stumble across something better.