I got the TacStar from Ajax :
http://www.ajaxgrips.com/vn/tacstar/...YytvgyZw78qRAg
The Choate I got from Bushmaster :
http://www.bushmaster.com/shopping/s..._extension.asp
There are other places selling these as well as at the gun shows but Ajax was the lowest I saw for TacStars and I've had good service from Bushmaster (not always the cheapest).