I know that there is no option within iOS 9 to get alerts for missed calls, but is there any app that will do this? Even a paid app?
My older phone (which I had until I got an iPhone in 2012) would beep every minute or so after a missed call alerting me to look at the phone. On the iPhone, the only way to see that you have missed a call is to actually look at the lock screen.
I have looked online, and did not find anything, but I thought I should ask here in case maybe someone else knows something or has a way around it.
There’s an app called “Missed Calls” which will periodically alert you if you missed a call. It does exactly what you want.
HOWEVER…
It only works while the app is active. So the app must be running, and the phone must be awake (not in sleep/idle mode). That is due to limitations set by Apple, to not let apps really “do” anything unless they’re active.
As a result, that app and basically any app trying to do what you want is useless. And the iOS has no built-in feature for this, so you’re out of luck. 
Ah, that’s what I feared.
Guess I’ll just have to hope the next OS has that feature (not holding my breath on that.)