It's very depending on which apk you want. If you only want the apk of one specific open source app, just check on fdroid or on their git (mostly on github). And if you want play store apps without installing Aurora store, just use ApkMirror (their apks are mostly clean, cleaner than Apkpure in any case..).
actually paid $3 for this app like 5 years ago but the fact that it's missing from all the official locations means I'm going to have to pirate it to get my $3 back