I am not sure about online, but I looked up the number and called. You can get it at any stage of pregnancy. I believe I was 5 weeks this time. When you call they will give you a appointment, and tell you what you need to bring document wise.
No I don't think you can do it online. Just call the number and they will give you an appointment. And bring all the info they tell you to bring. And you can be any week.
Like they said .. i started gettin wic days after i found out i was pregnant.. lol called made an appointment and showed up signed papers.. got some free goodies and alot of papers about pregnancy breastfeeding and eatin healthy.. good program!