“Where does one go to seek a valid annulment?”

Thanks for your question.  It’s important for people to remember that there is no such thing as “an annulment” of a consummated marriage, but only a declaration of nullity that a certain union never was a marriage to begin with if there is clear-cut evidence proving that a particular union was not validly contracted. 

Canon 1014, 1917 Code of Canon Law: “Marriage enjoys the favor of law; therefore in doubt the validity of marriage is to be upheld until the contrary is proven, with due regard for the prescription of Canon 1127.”

Since there is no Catholic who can issue such a judgment at this time, one could only apply the principles to an obviously invalid marriage.  In other words, if two people go through the motions and apparently contract a marriage it must be considered valid and binding unless it’s a clear and obvious case that it wasn’t a valid marriage (such as that one of the parties was already validly married to someone else).