Antique Phonograph Supply Company (APSCO, they now have a nice web page)
will do spring lube and/or replacement.  They have a lot of experience
and use new stock if the old spring is broken.

That being said, if you are adventurous, the safest way I have found to
unload a spring is to get a big plastic garbage can, hold the can over
the edge and bang it a couple of times.  Much sound and fury ensues, but
the spring generally heads down into the can.  Remember, kids, don't do
it unless you are a licensed professional.  Rewinding is not all that
difficult if you are patient.

A. B. Bonds