The real thing:
...and this is an HD picture of the same:
http://www.bbrclub.org/Barrage%20Bal...ssel%20adj.jpg
its american counterpart:
I think both british and US barrage balloons were silver grey in color, as shown in this other color picture:
Finally, this is a model for sell at TurboSquid:
Thanks to you, Trevally, it seems that we have just spared 60 bucks
This is the TurboSquid page with some more vies of the former model, just in case you want to get inspiration from it for adding some more detail to your creation