Don't know how the "free" market is by you (we live in the Fort Lauderdale area) but I've seen a lot of Craigslist postings for pavers, stone; building materials of all kinds under the "free" category in our area.
I think that may be because there are so many foreclosures, that when people are clearing out of their homes and leaving things behind. There are also a lot of unfinished projects being left behind, too; stone and wood and windows and such piled in backyards because something got started and the money ran out to finish it.
You may also want to check out Freecycle and get yourself on the mailing list for your area group, and post them as wanted. If you still can't find anything, consider finding your closest Habitat For Humanity building supply thrift store. They are always getting something in, for pennies on the dollar as compared to what you'd normally pay retail.
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