If that were true then it wouldn't even matter how big or small the Protectorate got as an organisation, since they don't have the item in question. Grabbing any given Protector anywhere in the galaxy and taking their stuff would be enough, if they had no proper support network outside of Earth. And a Protector's job is to protect; it wouldn't be especially difficult to find one, their role makes advertising their presence more or less essential. All of this is of course assuming anyone would actually care to steal a Matter Manipulator, which again, there isn't really anything to suggest is the case. Your hypothesised inability of the Protectorate to find enough people to train could be attributed only to an unwillingness to expand. If they were of sufficient size and had sufficient influence they would be able to develop more talent. The more people you have the more manpower you have to train more people.