It seems there are a couple things about the 4Runner's design that make large flares difficult. I'm still waiting to see if Bushwhacker comes up with anything.
Most of the vehicles that have aftermarket flares don't have a removable flare section from the factory, and if they do the flare normally only covers the top half of the wheel well.
The 4Runner's flare extends down to the rocker panel, and is also incorporated in the front and rear bumper which I'm sure becomes a nightmare when trying to design and aftermarket extended flare.
Like others have said best bet if probably Trail conversion.