Could somebody tell me which organic salmon farms in the world are using closed pen techniques?

I think you're going to need to do some research, Harriet. A Google search brought up no results for "Organic salmon farm" "closed pen". Another wrinkle is that standards for certified organic vary from country to country. Many say that confining salmon can never be considered organic, especially if the feed involves damage to ecosystems in other places.

I think you are right Jeffery, there is lots of talk but no systems in operation.
We must remember that no organically produced salmonid fish species has access to a natural food supply, unlike any other organically labelled animal which has.