Pachinko games are much like other electronic devices (e.g. Computers, Televisions, etc.) and contain hazardous materials that do not belong in a landfill. For example, components are assembled with lead solder and contain other heavy metals which can contaminate the earth.
The Environmental Protection Agency (EPA) has information about electronic product recycling programs. Your local community may have a recycling program, too. Check with your county or local government, including the local landfill office for regulations.
Alternatively, Pachinko enthusiasts are always looking for new Pachinko games (both working and not). Consider using a listing site as opposed to disposal.