You will gain some more BF but will also gain more muscle. Generally people work in bulk/cut cycles to get bigger/stronger. Check out the nutrition forums for some solid advice.
Try and reach out to a local Crossfit gym and see if they can teach you the lifts. I know it's not the best resource but I doubt you'll be able to find a real Oly coach...
Yeah, fat is extremely easy to find. As far as fish - those 3 you named are great. Salmon is delicious and super versatile. I personally really like sardines too but it's not everyone's cup of tea....