For the disk Brake check your local bike shop and you can get one pretty cheap there. i just had to get a new one recently and it costed 42$ for the whole setup besides the lever and cable along with a rotor.
the rack you could also look at the bike shop for a nice aftermarket bolt on for cheap, or you could go on the Schwinn website and see if they carry racks.
the other two i dont know about. good luck
