3, 4, 5 & 6mm stainless I get from Noggin End is pretty straight although not ground. Its fine for shafts (for me) but if you want hardened (and smoothed?) stainless shafting try IGUS. (http://www.igus.co.uk)
Originally known for their polymer bearings they now have a wide range items including linear bearings and shafts.
I've no connection other than being a customer.
Ian
Edited By Ian Phillips on 12/05/2012 22:38:12