Hi Darren,  For a substitute or replacement winding key, you might try
one of the longer ornate (decorative, antique, vintage) gas fireplace
valve keys.  If the aperture is a wee bit too large you can shim the
interior walls to achieve a tight fit.

P.S. For ease of winding, a modified (long shaft) 1/4" socket wrench
in a small ratchet works wonders -- almost like winding a cartel box!

Best of luck,

Don Caine - The Music Box Repair Center Unlimited
Lomita, California
http://www.musicboxrepaircenter.com/ 
mbrcu@aol.com.geentroep [delete ".geentroep" to reply]