I recently misplaced my iPad, but was easily able to locate it via the finder app provided by Apple! (I had left it at a restaurant, and had it back within 24 hours.) Is something like this available for radio equipment?
We 'lost', er, had stolen an iPhone in Chinle Arizona while visiting nearby Canyon DeChelly in the Navajo Nation. Using the iPad, we tracked it to a specific residence and had connectivity just long enough to lock it out, rendering the absconder's new found toy essentially a brick. We contacted the police and they did visit the home, but the residents denied any knowledge. Officer told us that was the end of any recovery attempts. :/
They do make GPS tracking devices for pets that work through the cell grid. Waterproof, shock resistant and designed to be small enough for a dog to wear, think Lo-Jack for Fido. One could possibly install it in a radio if there's enough room inside. You'd need to make provisions to charge it and I'm not sure how well the signal would penetrate a metal enclosure.