Wow guys some awesome discussion here!
First, MJ's suggestions. The only corrugated tube like in your second picture that I've ever seen that might be small enough is from Lego Technic sets. I'm sure I've got some around but from my Lego building days I still have a disagreeance to butchering Lego
The woven tube at the top is an interesting one, and similar to something I have always intended to use on a model. The material pictured looks like a woven tinned copper, however you get a similar texture in fibreglass insulating sleeves (used in electric stoves and such where you need an insulation that won't melt):
The problem is that it won't make for the kind of tight radii we need for hobby work without kinking, so my idea was to fill the tube with clay, mould it in silicone and then duplicate it in flexible polyurethane tinted black.
Joey; that's really interesting to know regarding tempering the guitar/bass strings. I have a mini blowtorch at work so it would do the job quite well. The absolute thickest available bass string would probably actually be approaching the right diameter.
But the thing is that this is all a lot of extra work that I feel is a bit unnecessary: why does the mega bolter need big power cables? It should barely need any power at all - all that is needed are to run the gattling and feed motors. The plasma blast gun obviously needs lots of power because it's not firing a solid projectile. So I think I'm just going to mod the rear of the mega bolter to hide the cable entries.
Joey I can definitely make you up some grilles - I'll swing you a PM
Oh yeah I can make that....