I’m an EWTN missionary.
EWTN sends me schedules every couple of months, and I stuff them in our church bulletin (with my pastor’s permission of course). A couple of times a year (Holy Week, Christmas) they send posters to put up inside the church entrances. I also make available EWTN promotional material (schedules, posters, and whatever else they send me) at our parish feast’s evangelization table.
That’s probably typical if EWTN is on your cable system. If it isn’t, of course you can organize an effort get it put on, or work with those who have already organized such an effort. If there is a group working to get EWTN on radio in your area, you should support their efforts as well.