Do keep in mind that the OP never said they were to be used as drive wheels. They may be for a lower load application (intake wheels, ball handling, follower wheel, etc).
Banebots sells 4.875" wheels, though I wouldn't recommend using them as drive wheels.
http://banebots.com/c/WHB-WS-498
McMaster also carries a large variety of wheels, many of which come in a 5" diameter. To get the wheels most similar to the AndyMark KoP wheels, select a rubber tread and a "soft" durometer. Granted, these wheels are not designed specifically for FRC competition or interactions with AndyMark or VexPro parts, so some modification (namely broaching and/or drilling a bolt hole pattern) may be required.
http://www.mcmaster.com/#standard-wheels/=qdt1ol