209 conversion kit

I have an older kinight muzzleoader that I love to shoot, its accurate, but I have had a few issues with the #11 caps. I found a 209 conversion kit I was thinking about getting for it, but its a .54 caliber so I'm having some issues finding bullets for it where I live now. The kit costs $39 but should I just save up and buy a newer .50 cal or do a few upgrades to the older .54. It has a 1 in 28 twist rate and shoots conicals like no other, but I have heard great things about t/c shockwaves and barnes expanders, but they are .50 cal. Do they make empty sabots I can just put the shockwaves into instead of the ones they came in?