Anywhere that sells rubber and sponge and seals should have something. The hose sponge tubing is easy to find, just need one that's good quality and retains it's shape. And of course if the lines are still connected then you may have to slit it down one side and use a bead of silastic, look better than zip ties. The larger muffler cover might be trickier finding a tube the same diameter, on the plus side, you could wrap it with flat sponge sheet and tape or glue the join underneath and not be seen.
