Kim, the chemist sells folic acid on it's own, i used to take 'Nature's Own' ($6.95) for the last 10mths pre-conception and once pregnant i started taking Blackmores Pregnancy Gold tablets (1 morning, 1 night) i would start on those if i were you

But don't panic, as long as you are eating really healthy and eating foods that are rich in folic acid then you are pretty fine and you've had two healthy bubbas already as well perhaps look up on the net some foods rich in folic acid (folate) and get straight into them.