If my wife and have been separated for many years but she is not willing to go for divorce, can I at least get a legal separation?

There's no such thing as legal separation in New Jersey. The closest thing that we have to that is call a divorce from bed and board or otherwise known as a limited divorce.  This is a divorce process and does not terminate your marriage entirely. Instead, it allows you to resolve your financial and child related issues but still remain, technically, married. 

This process is typically used by people who are either very religious and cannot have a divorce or those that need to maintain medical insurance would not be able to do so after a divorce.