D.M.
My husband had the same problem with his ex wife. Every time he'd have the papers ready, the server couldn't find her. After enough time his lawyer went before the judge and pled for an uncontested divorce, and got it, seeing as how no one could seem to locate her.
Honestly, I'd suggest calling around and seeing if you can find free legal aid. They can point you in the right direction for notification, and drawing up the papers yourself is a whole lot cheaper than hiring a lawyer. I would also suggest calling around for divorce specialists in your area. Many lawyers provide a free consultation, and that can also be an enormous help. Be sure to outline in everything how long you've been married, how long you've been trying to divorce, how many attempts to serve him papers there have been to date, etc.
I cannot stress enough, document everything. It will be a life saver in the end. Even if you end up drowning in paperwork.
Best of luck!