Hmmm, it came up just on my iPad Air 2...sorry it didn't work for you. I really don't know why.
Ok, one more try because it's definitely on my iPad...do the following exactly as I state and it should work:
1. In the search field, type in "photoblend pro" (no quotes)
2. Do NOT select any of the displayed results at the top-right of the screen. Tap on the blue Search button at the bottom-right on the keyboard.
3. Tap "iPad Only" at the top-left and change this to "iPhone Only"
The first two results at the top of the screen should be "Photoblend Pro- Double exposure" and "Photoblend - Double exposure.