I am not sure exactly what you are looking for Magda as there seems to be a variety ...try this link   http://www.migem.com/Categories/Peru_Opal/blueopal1.htm or you may want to try ebay...good luck!  Be sure to scroll down after clicking on the link as they have some very beautiful strands.

Hi Magda, I got some really lovely ones on ebay, one strand of facetted, and one strand with a graduated colour, I believe that the seller I used is called Chakras.

HTH x