A few thoughts on the subject;
1) True Love, to be the White Court catch, needs to be from both sides. Not someone truly loving somebody else but two people truly loving eachother. If true love is as rare as true magic, say 1 person in 10.000, true love that is returned would actually be as rare as 1 couple in 50.000.000. (naturally, true love is not as rare to begin with so true love in couples would be somewhat more than 5 couples in North America).
2) Such love has to be "consumated" AND confirmed to funcion as the catch; Justine only functioned as a catch after nearly sacrificing herself for Thomas - they both have had sex before and they both loved eachother but it wasn't a catch. Though not confirmed in the books, I believe Harry and Suzan's love was confirmed as True after Harry was willing to sacrifice everything for her, even in the face of a war with the Red Court.
3) It is very hard to weaponize true love. Items can be blessed for Faith, silver can be fashioned to bullets, fire and other elements can be replicated by magic and technology and so forth. True Love cannot become an actual weapon. Yes, a ring or personal item might cause pain but wound not burn the target outright as the actual person's touch would and said items have to be important in said relationship (i.e. a wedding ring or a favorite gift not any ring or locket) and said lover selling or giving them would automatically mean they aren't important enough.
4) It is impossible to recognize someone as White Court vampire before they use their powers. So you can't research it in advance.