good source for steel or iron machine screws for magnetic pickup pole pieces?

[Mad Scientist Jr]

I thought I was lacking magnetic force because a screwdriver did not
stick to the pickup pole nearly as strongly as it did to a regular
single coil pickup.

but after much playing with different magnets, I had been playing with
this other project, a simple preamp from this schematic -
http://www.electronicsteacher.com/circuits-and-diagrams/audio-preamp-circuits/preamp.gif

which I attached my homemade pickup to, and voila! It now sounds
louder and clearer than a regular passive pickup.

So I guess my design works ok for an active pickup.