Its really hard to say without seeing video of your skiing, or even squatting so we can see how bad this is.
I would guess, without seeing video, that the issues you have skiing are not really a result of being duck footed.
Like bruce said most boots can be rotated a bit.
(disclaimer, the below could be wrong for you and its impossible to say without seeing some video)
For corrective exercises, work with a PT, but most people with outward pointed feet also have collapsed arches and valgus knees. It takes a long time to improve, I've had success doing squats maintaining external rotation through the knee and into the foot (this picks up the arch) and constantly being mindful of keeping the knees pushed outwards during squats (middle of knee tracking over or just outside second toe)
These are a couple common methods that could help, but you should consult a PT and post some video here of your skiing.