Mystery egg?

[Kontana]

I read that you could get it from an officer by trading a growlithe in the police station, and the officer in the counter seems to want one but doesn't mention anything about a trade, would i need to have a certain amount of badges in order for that to change? or do some event?

[Plok]

talk to the officer that is placed opposite of the one that is at counter

[Tacos]

Also, just going to point this out since I managed to miss this important part, you must have a growlithe egg and not a growlithe.