AFAIK, this is the limitation of using old devices. If you owned the device when it was current, you have the apps backed up in iTunes. If you purchase an outdated device, your choices are severely limited. My old 3Gs is still viable only because the apps on the device are stopped at the versions that correspond with iOS 4.3.5 (iOS wasn't upgraded due to concerns about potential performance issues.) IDK if the app developers could even help.
BTW, not much time passed before you bumped your post (forum rules prohibit this.) I just saw your thread; likely the same for others.