Hiya,
I would guess that the steel is something like silver steel. This is readily available in 300mm lengths and is ground and polished in its standard form to extreamly tight tolerances. I know you can get 6, 7, 8 mm diameter the tolerence on the diameter is something like 0.0025mm;
If you google silver steel you will see what I mean.
hope this helps or gives some ideas for you.
cheers
Lee