Third parties are allowed to use the Find My network. I have a Find My "credit card" in my wallet made by Chipolo.
And a 3rd party tool that does even more: https://play.google.com/store/apps/details?id=de.seemoo.at_t...
What OP means is that I cannot purchase an Airtag/Chipolo, and then subsequently find that Airtag using the Find My Network with my Android device.
I can identify airtags around me with that App, but I cannot locate a missing Airtag.