A.S.
Hi Dawn,
Congratz on the pregnancy, I am 12 weeks today! ;) Craigslist.org is a good place to start. Just in the last three days, I've seen probably 3 or 4 different people post maternity clothes. It's not exactly what you are asking for, but it is something. The ones I've seen were actually under 'baby and kids', but you could check 'clothes' also.
Good luck!
Amanda