On route 3, ( the route to left of Striaton City), is the pokemon daycare, you can breed pokemon there by putting a male and female pokemon of the same egg group in the daycare to be raised, and after awhile, come back to the daycare and talk to the man in front of it and,voila! he will give you an egg! the egg will hatch anywhere between 1,000 steps and 10,000 steps, so it might take a while to hatch it. the egg groups for breeding can be found here:
hope this helps!
also, if you happen to get a female starter, breed the crap out of it, as people will be more likely to respond to a trade that isn't asking for a level 9 and lower zekrom, so you can get some decent stuff that way on GTS trade.