@col.bris: I think the OP is saying they've never downloaded Find my iPhone before. It would not be in the Purchased tab unless it had been downloaded at least once. Most people think of this a buying, even though it's free, since you still have to tap the button and enter your Apple ID.
Still, I'm surprised that the older version of the app does not show up in the App Store on the iPhone. You would think that Apple would include their own apps in the ability to download older versions on older iOS devices. That was supposed to be an ability that rolled out at the same time as iOS 7.
@Husq250: I'd contact iTunes Support and ask. Make sure you contact iTunes support (free) not Apple Tech Support (not free).