Mailing all those letters was an awful lot of work. If you feel up to it, you may try faxing a bulletin announcement to at least some of those churches. You can fax from your computer and send them all at once. All it takes then is a church secretary to who'll put it in the bulletin. Include your email address as a contact. There are usually one or two active (or people who feel they should be active)pro life people in a parish. If you can have one or two people in a few different churches that you can count on, you've got a group.
Unfortunately, sending out a cattle call is going to get you a lot of sad, lonely, often old people who really can't be much help to the pro life movement except perhaps as prayer supporters (and some guaranteed time off in purgatory for the rest of you).