Two things.
1. There are about 25 million iPads sold in the world. Now this may seem like a lot, but if you think about it there needs to be a demand in order to make an actual app for the iPad. Nowadays almost everyone has a smartphone so that is why they have apps for both the iPhone and the Android phones. The demand is there for the phones, but not tablets. . . . yet. With the iPad it is different because not everyone HAS one.
2. If you are hungering for Facebook integration why not just tell all your friends about it on there? Just post on your Wall, "I like Geocaching". Those that are intrigued will probably ask you about it and those that don't, oh well. Or, even better yet, why don't you take some of your friends on a geocaching trip? They will know how much you enjoy it and might even want to go on more expeditions with you.
That's my two cents.