I think I have some 17" square ones if you are interested, I can bring them to the swap

Yes, please. That would be great.

There is this place where you can get them for very very cheap in Sumner, WA. They sell flats by the lbs, it cost $2 per pound!! The website is http://mcconkeyco.com/

(McConkeyco dot com)

You just come in the show room, pick your flats (several types, sizes) weight them and pay at the office desk.