No luck friend. Checked all the usual sites i go on. Even a Google search on the package name just brings up two results for APK sites, apkpure and apkcombo both of which will direct you to play store because it's a paid app. These exotic apps as you call it sometimes have extremely good security because they charge a fortune for the app because they are only ones offering that type of app which then of course means they have more money to spend on protecting it. I recommend once you buy this, copy that APK asap, save it somewhere else, make another couple of copies and uninstall the play store version BEFORE the refund and test the APK first. You get one chance at refund in play store and it won't appear again if you buy it thinking you will keep getting refund. If APK works, go straight to play store and get your refund and reinstall the APK. If it doesn't work then only option is to modify one of the copied apk's you made earlier. That's why I recommend making a couple of copies so you always have the original to fall back on.
If this app doesn't have any in-app purchases then the chances are very high this app will have a licence check because if it doesn't everyone who wants this will be downloading it and 5 minutes later request refund and Google don't like giving anyone their money so would tell app developer and get them to put a licence check on. Then you will have to modify the APK and non root this option isn't very successful I'm afraid.