I have not had a chance to shoot mine yet (got it at the gun show last weekend) but J & T distributing sells the 300 whisper. They are a little more expensive but from what I read on ar15.com they are supposed to be better quality than the M1S. Plus they stamp their barrel "300 whisper" instead of the knock off names.If you want to see a pic of my build then go to:
http://www.geocities.com/underwatersniper/whisper.html
Completed upper + Lower kit (minus stripped reciever) +jewel trigger +tax came to $722 with a 5% military discount. They do not have them listed on there website that I could find but according to them they have been selling the whisper for over 2 years.
Hopefully I will have a range report this weekend, I have to see how brass forming goes as I am making them from Lake city 5.56. The brass has been trimmed and its ready to form, My dies shoould be here tomorrow. :D
While talking with them he brought up a good point that I have never heard before: he stated they feed more reliably from a straight magazine compared to the curved 30 rounders. I guess I will see if the 20 round straight mag works reliably this weekend.