You did the trade you feel you came out ahead, it's a done deal don't try to argue your point with anyone. However, next time you go to make a trade do a little research and it'll save you a lot of headache. If you don't reload you should always take ammunition availability into consideration before making a firearm trade or purchase.
I'm sure your father will help you, especially since he traded you the rifle. Don't over complicate things, go out and shoot and enjoy your new rifle. Let us know as soon as you do how she shoots.
You don't need .358 Win brass, all you need to find is .308 Win brass and you'll be golden. Then all you need to do is run the brass through your .358 Win sizing die and you'll have properly sized brass. Besides you have 100 pieces already in that Hornady ammunition that you got with the rifle. You'll be able to reload them a few times before you'll need different brass anyway.