The flash tube is an MPP flash. Unless you're fixated on a found parts build there are plenty of lightsaber replica that will fit the bill and will be much cheaper than the MPP, which you'll have to find first. There is a MPP flash on ebay right now and it is the correct tube but the seller wants 1300 quid for it. I'll be amazed if he gets that because despite his listing that it's an accurate original for the Vader saber the no step shroud, the big selling point for the MPP, has been altered and a replica one included which completely misses the point. It's a shame because the other pieces for the saber are correct.
The barrel mounts sidewinder sells are based on a plastic 'Maclow' clip and a plastic 'swimming pool clip' that came out of a discussion in an old thread. Lonepigeon and I came up with those suggestions but it was a group thread effort. Bear in mind they're not the right parts but simply the best we've got to so far. Sidewinder's replica are pretty nice although I'm not sold on the rear clamp under barrel two plates joining idea but as I'm in a minority of one what do I know. The Combatbaby aluminium versions are nice if you want aluminium pieces but they don't look close enough to what is seen on the prop for my money. I have no idea what the little blocks atop the barrel clamps are. I've done some research but nothing fruitful. Mine are Sidewinder versions based on his scratch build.
Molex have been mentioned.
Known stock greeblies are Hirschmann LMK/AM Aerial/Earth Connectors (Model No. 730 851). You need four, not three.
Centre stock greeblie still unknown. Various theories. Most people use something based on a scratch build. There are some nice looking 3d print versions out there.
Sling is a rubbish old strip of leather and likely not the original sling, which would probably have been a lanyard.
Revell V8 visible connecting rod has been mentioned. If you've been smoking guano cheroots then this will have to come from a vintage model with the electric motor. If your cigars are a normal brand then buy the modern, cheaper and easier to find, version; it's the same part. Part number is 65 IIRC.
The breech greeblie is some sort of unknown disc. I doubt we'll ever know what it is. It is absolutely not, not, not part 107 of the Revell visible V8 (pulley front half). That part is too small.
Scope is could be any one of a number of vintage 4x20 scope brands. This will be popularly referred to as the ASI scope as ASI was the first brand match found although this is almost certainly not what is on the prop. The most likely brands seem to be HUNTER or MILBRO (Millard Brothers) but it really won't matter so long as you marry the correct scope model with the correct receiver rings. There are 13 or 14 confirmed brands; I forget which.
If you have found a real Webley then a found parts build should be the goal. It deserves no less!
Peace.
Andy