I think you just have to get a pharmacy to order it for you if they don't normally stock it. I believe you can also buy it online from drugstore.com. (I don't use Neocate but knew someone who did.)
No. Neocate is not a prescription usually. You can ask for a script if it will help you get it covered by insurance, or WIC, but it is available over the counter. A similar formula-EleCare is prescription only. If your insurance won't cover Neocate, you can ask about EleCare. EleCare actually has "medical food" written on the canister and sometimes that makes all the difference to insurance companies.
Re: Neocate
DS's GI calls it in as a prescription so that way the insurance covers it for us.