Can't recommend anything from personal experience but i know that flax seeds and chia seeds are supposed to be high in omega3. Also there's an interesting article you can read here http://www.veganhealth.org/articles/omega3 that talks about omega3 for vegetarians that's worthwhile reading.
google a supplement called opti3. it's an omega 3 thats suitable for vegetarians and vegans. i got some from an online vegan store (can't remember which one) but im pretty sure you'll be able to find it if u google it.