B&Q do sell threaded rods and stuff, the trouble is finding it in the right thread size. Bolts are the normal source of standard thread sizes which you can hacksaw to required length, but unfortunately they'd most often be steel which is an issue. Perhaps try electrical stores like Maplin, they might have threaded aluminium inserts. Your school DT department would probably have the M8 x 1.25 thread dies you need so they might be willing to help.
Tap and die sets are always nice to have, maybe an early birthday present

Thread cutting with a manual ring die is always tricky because it's hard to get it straight, so make sure you give the rod a bit of a taper first and then thread it.
Or perhaps Nev could whip some up in a jiffy in exchange for beer or a cookie... I don't have a tap and die set unfortunately

Chiok