kosher asian fish sauce
Hi there.. I have not found kosher fish sauce, but I use the following recipe with good results. (Note that this is good IN something, like pad thai, and not so much as a dipping sauce).
Mash 6 anchovies (well rinsed and drained) with 1 clove of crushed garlic and 1 tbsp. soy sauce in the blender.
You are not the first to ask about kosher fish sauce. It seems that it might not be available. I know that the topic was tossed around on egullet with no luck. I have a friend who is an expert on hard to find kosher foods and will drop him a line to see if he has heard anything to help you in your search.