If the app is gone, it has either been removed by the app developer or by Apple.
The app is gone.
If your iPad has been stuck on iOS 10.3.3 for the past few years, with no upgrades/updates forthcoming, then you own an iPad 4th generation.
A 4th gen iPad cannot be upgraded beyond iOS 10.3.3/10.3.4.
A 4th gen iPad is a nearly 7-1/2-year old device, now!
Its internal hardware is too old, underpowered and completely incompatible with any current and future versions of iOS.
Sorry. It is what it is at this very late date.
These old iPad 2,3, 4, 1st gen iPad Mini models are nearing 8 and 9-years old, now.
As of the beginning of 2019, many, MANY third party app developers are all more quickly and completely dropping older app support for all old 7, 8 and 9-year iPads that are running 2-3 year old and earlier iOS versions.
Third party app developers are removing all of their older, legacy versions of their apps from Apple's App Store servers, now.
Older versions of apps are going to be gone for good, now!
Getting older versions of app for these old iPad models, initially from Apple’s iOS App Store is getting to be very difficult and problematic, now, and will only be getting much worse in the year 2020.
These old iPads are now reaching their complete end of life and support.
Old iPads that can no longer be upgraded/updated will have NO MORE APPS AVAILABLE for initial download, at all, soon, from the Apple iOS App Store, for such old iOS devices in the very near future.
Older versions of apps for older iPads will be completely gone, very soon!
Time to now seriously consider a new or discounted, refurbished iPad from Apple.
Sorry & Best of Luck to You!
