I thought that you do NOT need a sponsor to take the series 3 exam. Can someone confirm that? I am not a US citizen and when I try to register for the series 3 online (prometric) it asks for a social security number which i don't have and it says that for non-US citizens you should ask the compliance dude of the sponsoring firm for a number to enter into that SSN place. So I am not a US citizen and I do not have a sponsoring firm, I cannot proceed without entering a number...huh?
I doubt you will find many who are registering for Series 3, are not citizens, and have any clue what the answer is. Seriously, try them first. or maybe do a very focused internet search.
You definitely do not need a sponsor to take the series 3 exam if you are a U.S. citizen. If you are not a citizen and do not have a sponsoring firm and no one else can answer your question, then you probably should contact the NFA and ask for clarification of what you should do. It is conceivable that unsponsored non-citizens are not eligible.