You don't stuff it, you wrap it around the core of the silencer, then hold it in place with a little bit of tape. Then slide the core back inside the housing .
I got a repacking kit from Fly Racing for my FMF equiped XC 200. It was reasonably priced and had good instructions included.
Most of the suppliers of repacking kits are pretty much the same, probably. Just find something that's available in your area.
RB