Grouse Man, I use both Gamebore and RST shells. Gamebore from Kent as has been noted and RST from Prophet River. Gamebore is now special order from kent so look to the UK site to figure out what you want, then order through your retailer....expect a long time coming.....once a year.
Prophet River stocks some RST but generally to get stuff like felt wads and paper shells, that is special order as well. And again, don't be in a hurry.
It seems to me that the Gamebore stuff packs a bit more of a punch than the RST but on the upland I hunt....woodcock, ruffed grouse, huns, sharptail and pheasant, they both work just fine.
I keep a mix of paper and plastic hulls, felt wads and shot cups, in shot sizes from 5 through 8 and mostly in 2 1/2" in 12 and 16 gauge. I also tend to have significantly more than one season's complete supply on hand at any one time. I order once a year, usually after the season when I can see what I am getting low on, and that usually gives them plenty of time to get in whatever oddball thing I am asking for. Works well once I got the basic inventory laid in.