Changing Interests After Getting Accepted for PhD
Changing a subject during the PHD course is legitimate, and not very rare. However, finding an advisor is a must. I think in that case you'll have no choice but trying to convince professors to be your advisors. 

A possible way is to find an expert from a different university, that will be your co-advisor. That way you'll just need to find another faculty in your university that is not-too-far from your interests. You might find someone that will tentativly be your advisor, and once you show some progress will agree to take you under..

But maybe the big question is,
why not moving to the place where the "experts" are?