i saw some site showing that you could use the springs inside a vhs tape for the steering, haven't tried it myself, but you might want to look into it.
i found springs that are non magnetic for slot cars. 1.59$ for four of them. check a hobby shop that sells slot cars. its a lot thinner than a vcr spring. i only sort of got it to work tho. i also saw some site that sells steering springs but i dont remember the url.