Sierra .30 cal 240 grain matchkings never really took off. You don't see them around much. They do make a pretty impressive sight though sitting next to an empty .223 case (try it ;-)
In case you don't already know this, they are not a particularly high performance (dragwise) bullet. If you are looking for an extra-heavy, high-BC .30 bullet, there are better choices out there (the newly introduced Berger 230 Hybrid looks interesting). Then again for something like a .300 Whisper the 240 Matchking is probably a great choice. Best of luck with whatever you end up choosing.