Is there any way to get Aurorus if I chose Tyrantrum 1st? Besides trading for 1.
The only ways to get one are: trading/GTS, and hacking
Sorry, those are the only ways to get one.
Hope this helps!
You could find a fossil I'm the reflection cave or getting it on GTS or wonder trade. You could also breed but you must have a Aurorus and you could Shout Looking for Aurorus in PSS
Other than that you cannot get one without cheating, sorry.