Unless you have something in your divorce agreement that says the custodial parent can't move more than so many miles, there really isn't anything you can do. It is an unfortunate situation, but your support isn't paid to ensure you get regular visits, it is paid to ensure your child has the necessities of life. That doesn't change because they don't live nearby. There is a new country music song out about this issue. In it one of the lines says something about how neither party would win in this situation. If the ex-wife turns down the really good job offer in Cambridge she loses, if she takes it, he loses.
This is really sad. I personally thing the custodial parent has a responsibility to remain living in the area they were in when the divorce took place as long as the non-custodial parent does as well. However, this is a tough situation. What happens when the non-custodial parent remarries. What if the person they marry is in the military and gets transferred someplace. That is not a choice at that point, you must move.
I have a problem with this because of my personal religious beliefs, but the Courts (in the US), don't have a problem with it. So, there really isn't anything you can do. Sometimes, when the children are very young you can prevent some of this, but it is very difficult to do.