if we start talking state actors then unless we're taking about pacific ocean island nations, or some of africa and a very few others you hardly need more than 1. in fact for most of the countries out there, except for the "lose face" aspect of it, it would take little to no effort (in terms of a country) to do it. i would actually hazard that most subnational entities could easily do it if it's in their interest as well. In fact, i could actually see a national governments "outsourcing" it to subnational entities just because that way if it came out it was a state actor, they lose next to no face at all, as well as being able to go "sorry, nothing i can do for you bro, they have their autonomy"