Umm... let me see....
Cannister body: PVC drainpipe & end caps availble from any DIY plumbing store.
Watertight cable glands: Brass compression fittings, available from any decent plumbers.
Sealed lead-acid batteries & charger, switch & rubber switch boot from Maplins.
Torch: Butchered Maglite.
Glass disks: Any glass cutters.
Cable: Any DIY shop.
Duck tape, silicon sealant, O-rings and the like: Any decent DIY shop.
See
http://www.oneandoneis2.demon.co.uk/DiveWeb/torch.htm for a few more details. I haven't had time to put a full-on "How to" guide together yet...
I WILL get a better torch body put together someday, so I can have it on a Goodman handle, but I've been busy with other things lately (The two week holiday and new weight system, for starters)