OK here goes.
First, the A-8A is a wonderful device because it is one of the few airborne sextants that allows to work with either the bubble as an artificial horizon or without the bubble, using the visible horizon. Still, don't think you're rich.... the sexant sells on ebay under $100.
Your device looks in absolutely great condition. Also, the fact that you have some tools and spare bulbs in the box is quite rare. From the shiny cable in the lid of the box, I have the impression that the device has been restored to some degree. Originally the cable is rubber, and by now must have become hard and brittle. NOt easy to see from the picture though. The tube in the lid is the battery holder, not the light tube. The light bulbs are in the device itself. You could also check the spare bulbs to see if they appear old & original, or a modern replacement.
The batteries you described as "No. 10 unit cell"...that's just one more denominator for what are very ordinary type D batteries at 1.5V. You can buy them in any nearby electronics shop. (http://en.wikipedia.org/wiki/D_battery
). They are used to light up the bubble or the drum for reading the value at night, as you set with the obvious switch on the sextant.
On the left is indeed the stow area for a spare bubble assembly. These are hard to come by. There is a bubble assembly installed in your sextant: see your last-but-one photo: the metal round part with single screw under the telescope (right side of picture).
This bubble chamber should probably be redone indeed; i.e. refilled with a liquid to create a bubble. This is not very difficult; I did mine just last week. If you are comfortable with tools and work carefully, it's no big deal. My biggest difficulty was in obtaining all the materials required. The liquid is xylene, and you'll need a hypodermix syringe+needle, a bit of shellac flakes, pure alcohol (96% ethanol) for dissolving the shellac. Tell me if you want to go this way and I'll help you best I can.
The tools on the left are supposed to be three. Although I have none, I believe they are (see picture 17 in the manual you have)
1. Counter lock wrench (to be found under the name plate, which you can slide away to the right)
2. Adjusting wrench (you seem to have this in the box)
3. Screw driver
Actually you can live & work without those perfectly well, but I understand you want it complete for display purposes. Can't help you there. Again, those are quite rare.
Additionally, under the metal clamp (top left of the box) goes lense paper for cleaning, any photo shop will sell you this.
Don't worry about sending the manual, I have that. I do not have the July 1945 Navigators Information File. Not sure what it is, but sounds interesting.