If for some reason you’ve uninstalled the play store and you don’t trust third party mirrors, you can use the adb tool do download the apk from another phone.
Thanks to this SO answer: How do I get an apk file from an Android device?
adb shell pm path com.android.vending
adb pull /data/app/com.android.vending-2/base.apk /tmp/com_android_vending-2-base.apk