As far as I know, you can only get HAs from Max Raid Battles. I’ve also heard that Brilliant Pokémon (those with a yellow aura around them) have a chance for their HA, but I haven’t heard any definitive evidence for this, so you’re probably better off going for raids.
A full list of which Pokémon spawn at which dens can be found here, and a guide to quickly finding the Pokémon you want can be found here.
Keep in mind that everything about the Pokémon is determined before you start the raid, so if you save when you find a Minccino, but it’s not HA, it will never be HA even if you reset (excluding changing your date). However, if you save when you find it, and it is HA, then you can reset back there if you don’t catch it and it will still be HA.