You'll be amazed at how much stuff there is on ebay, but you'll need to know the size/spec rather than the application.

I use these at ilkeston

http://www.k-engineering.co.uk/

And Derby / Burton /Tamworth

http://www.pughandsanders.co.uk/index.html

Between them - They can normally get anything you want

I would go for 10.9 grade if possible

Here's the bolt I'm after. Approx 105mm long, shank is approx 10mm dia to edge of thread. That big washer doesn't come off at all.

The end bit of the bolt is "waisted down" to allow for ease/ speed of production in the factory
I take it you are looking for another of these? This being a pattern.
I would go for a 10 MM X 100 MM 10.9 Bolt and get a suitable washer turned to accommodate the 10 mm shank.
All your local bolt suppliers will have this size of bolt - possibly in 8.8 grade (either cadmium plated or black)

Yep an M10 x 100mm will be quite a common size, but check how much of it actually needs to be threaded, and use one that's only partially threaded if possible. If you were keeping the original captive nuts then you'd want to check the pitch of the thread, it's probably a standard 1.5mm, but could also be a 1.25mm fine thread. But assuming that it's not fit for reuse, it won't be an issue.

Where you destroyed the nut and retaining cup, is access possible with a spanner so you can use a conventional nut?

Can you reuse the washers from the bolts you cut off, enlarge the holes either with a drill or a round file.

Aye - As Joolz say's ensure you go for a bolt (shanked) and not a set screw (fully threaded)
If you want more shank you may have to go for longer bolt and cut the thread down to suit
It all depends on whether the part you are fixing it to rotates on it
The washer can be cut from a piece of stock round bar (correct OD) and drilled centrally 10 MM

Found a breakers in Rugeley, Staffs, who'll send some genuine Ford ones out to me. £10 for a pair, delivered. Jobsagoodun!

Thanks for your advice though, chaps.