It is fairly rare that ignition components cause spark plugs to foul. It can happen of course, but usually fouled spark plugs are due to the burning conditions in the combustion chamber.
Fouling is caused by an engine burning oil, or one with a very rich mixture. In the case of burning oil, you would probably see the oil level go down steadily, and get some blue oil smoke out the back. In the case of rich fuel it would tend to run funny (perhaps) and might throw black smoke out the back. And it can be a combination of these two problems.
One of the cheapest solutions for a rich fuel mixture is that your air filter is blocked.
Tell us which vehicle this is, what kind of oil you have in it, and how much mileage is on the vehicle.