"Paul Ockenden" wrote:

Because of the way that a door frame has been built, I need an extra long
key
to work a rack bolt (a good 4 or 5 cm longer than usual).

It's the usual star type key.

I thought that maybe if I could buy a foot length of the star rod material
I could
cut it to the right length, and then simply bend a small handle into it.

Only trouble it, I've got no idea where I might buy the rod. Anyone know?

Probably easier to weld a short length of steel bar to your existing key. If
you haven't got access to a welding machine your local garage workshop
should be able to oblige.