i am sure spook or tp555 can cut/thread a longer one for you if you cant find one at 8" for a reasonable price, spook does some kickass work! i heard some company called ed brown made some but i dont know the twist may be a 1-10?
here is one also for $265 at 24" but again no twist rate shown
http://www.edstc.com/customshop.html
24" 300 Whisper SS bull NIB $265.00
24" 300 Whisper high polish NIB $255.00