If you have the Diya app (also called the Diia app), you can request gov documents through that. The App name is the cyrillic "D" + "i" + reverse R (Ya): Дія.
If you don't have the app already set up, it will be difficult to do so from outside Ukraine. For identity confirmation, you will need to provide a Ukrainian bank account in your name.
There are a few websites that offer "services" to get the Police cert for you, but I would not trust them. Things have changed drastically since the war and the information I've seen on those sites are outdated.
The best method if you do not have Diya is to go to an Ukrainian consulate in your country. If your country does not have one, try to locate one closest to you that you can travel to.
It is odd that you were DQ'd by NVC without the Ukrainian police clearance certificate.