Well, finding it is the hard part, now that you have found the Raikou all you have to do is encounter it again. To make it do quicker try flying to a centrally located place, such as Saffron City, and if Raikou is close, walk outside to the closest route, and see if Raikou moves to that route. If Raikou is farther away, just Fly back to Saffron City again. When you move to a new route, Raikou will only move to a route next to it, but if you use Fly, it will randomly appear at any route. When you finally get to the same route as Raikou, to find it quickly you could put a Level 50 Pokemon in the lead spot and use Repels. Try using a Wobbuffet as your lead Pokemon. I know that it is difficult to control how much damage you do with a Wobbuffet, but you should be able to get Raikou's HP down to a reasonable amount. Plus, Wobbuffet's Shadow Tag will keep the Raikou from running away. Give your Wobbuffet Leftovers for healing support if you have them. Also, it will help you to buy some Timer Balls, you can buy them on Island 2.