THere are several good commercial kers. The first that comes to mind is Missouri, then Montana, but then there is also Berry's and a couple of others. These are the ones I see the most.
I have only purchased and used a few from Oregon Trial, Montana, and Cast Performance and I did pick some up from Missouri, but I haven't used any of them yet.
Just be sure to slug your bores before ordering and you will know what size to get. You want at least .001-.002 over bore in order to keep the leading down. Depending on your velocity, under 1000fps you can get away with pretty much anything, over that you need to stick with something in the 12 BHN and up to around 18 at the hardest.
Mike / TX