Type into the Ebay search engine Vintage blinds NOS and see what comes up.  You might have to play with the word but I bet you will find what your looking for. You can also go to JoAnne's Fabrics' and get it.  Just make sure the size, width of the ribbon is right.  You can pick up cord there as well.
  It's a tedious job to do but when it's done it really does look great.  On my Little Gem I plan on ordering from Blinds.com  They have the best prices and are fast on delivery.