I am not a canon lawyer, so I do not know what provisions are available when one of the spouses cannot be found. I can only recommend asking your pastor to help you put your case before your diocesan tribunal, being completely honest with them about your marriage situation, and letting them decide what is and is not possible.
I do want to say though that it is problematic to nurse an attitude that, if your ex-wife cannot be found, you will be “stuck” with her. Keep in mind that you took vows to love, honor, and cherish that woman for as long as you both shall live. If, for whatever reason, an annulment is not possible (which may be the case even if you do find your ex-wife), the Church would be asking nothing more of you than what you already vowed to do, which is to live a life of marital chastity (no romantic relationships or sexual relations with anyone who is not your wife).
Granted, living a life of marital chastity without your wife would no doubt be extremely difficult and lonely. But you can offer up your difficulties and loneliness to Christ in union with his cross for your wife’s salvation. Such sacrifice would be meritorious for your own salvation; and, as a member of the military, you are no doubt already used to living a life of sacrificial giving for the sake of others. God bless.
