Not to many people shoot muzzleloaders anymore since they went to singleshot cartridge rifles.
You might look on Graybeard Outdoors Forums in the black powder section.
I'd try Blackhorn 209 powder. It shot great in my TC Impact rifle and cleans up easily and doesn't gunk up the barrel after every shot. An 80gr measured load is equivalent to a 100gr black powder load.
goex is black(gun powder) made here in Louisiana, but sold nation wide.
and i use whatever brand sabbot i find. ive been shooting inline muzzleloaders for decades. ive owned the tc prohunter, knight wolverine, knight american, cva optima. and the only difference i have noticed is if you get a .452/.50 mixed up in the .429/.50 bag.
i shot .454/.50 250gr bullet for a bit, but there a fair decrease in accuracy.