First off, I feel for you with 3 under 4. I have 3 under 6 and they are all boys. I just started finding time to do one hobby, but I have to do it with them because the 2 older ones want to help me (with fun things).
2 Questions. 1)Are you only allowing moms to sell or are vendors also allowed? 2)How much are you charging per table? I may be interested in a table if I can sell my products as well as normal mom2mom stuff.
There is a board at Charlie Browns in Almont, you can ask local churches to post it or include in weekly bulletins, look online for lapeerclassifieds.com (?) Post an ad in the paper.