I spent a lot of time looking before I found Biochem Whey Isolate Natural flavour (all of the flavoured kinds have sweetners). Unfortunately, they don't specify if the lecithin is from soy or not, but since its not noted as "soy free" I can only assume it is from soy. Regardless, definitely one of the least offensive nutritional contents I found for high protein AND low carb. It looks like the Vegan Protein they sell might meet your requirements, unless you are concerned with carbs.
http://www.biochem-fitness.com/pages/powders_main.html
(WFS)