The "shoots softer" argument is never proven. A carbine stock, with a heavy buffer, will shoot lighter than a stock rifle length buffer system. Using a short fixed stock uses the same buffer system as a collapsible stock.
If your just interested in a fixed short stock, your options are a bit limited.
The A2 Shorty Fixed stock
http://www.dsarms.com/A2-Shorty-Fixed-Stock-Black-----MALESTK/productinfo/MALESTK/
The ACE ARFX-Entry
http://riflestocks.com/store/product94.html
Both of those stocks are fixed length, with carbine length buffer systems.