Ruth, try eBay.  However, you'll probably need to find out what kind of
music box movement is in the original rocking chair.  My guess is that
it'll be the standard wind-up type with a mainspring, probably 18-note,
1-tune (one "air").

I've purchased over 100 of 18-note, 1-tune Swiss movements on eBay for
around $2.00 or less, usually several movements in one lot.  Sometimes
it's just the movement and other times it's the whole music box.  I've
also purchased nicer movements with more notes and more tunes on eBay.
You can figure a 28-note, 2-tunes movement will go for around $20 to
$30.  More notes, more expensive; more tunes, more expensive.

Good luck.
Randy Faerber

 [ Thorens rocker movements of 1952 are pictured
 [ at  http://mmd.foxtail.com/Pictures/thorensCat.html
 [ image  http://mmd.foxtail.com/Pictures/thorensCat4.jpg
  -- Robbie