Call for Artists, Making Money at Juried Art Fairs, Craft Shows and Festivals
We bought ours in a used office supply store, where they had been classroom desks.
Don't know if you've found what you need by now, but I have two 20" x 48"s from Samsonite that I got on craigslist years ago. Been very happy with them. Don't know if they still make them.
walmart has 18 inch tables
I recently ordered some tables from Coleman which I saw on amazon. They are 31.5 x 15.5. The legs are adjustable to three heights. I like them, but they are not really strong---I am not sure what you are putting on them. It is called something like a "Packaway 4 in 1 table.
You can hook the two tables together to make one square one if you want.
some folks have covered "beer pong" tables which are the right size and fold up nicely.