That MIGHT work for you, but they will take just as much of a beating as the radios you stated above. Are you talking about a hospital style paging platform? You can find those, and extender anntenas online. They are called "StaffPage" systems. Be prepared to pay just as much for the complete pager system as you would some paging horns.
This is an example:
StaffPage Remember: This one costs less because it does not handel alphanumeric messaging or a screen.
