we bought some kind of pressure-treated but otherwise cheap pine-like (fir?) wood from a Home Hardware. The Spikies were just realy big nails hammered into the top, with the exception of our ridge uprights, which Scott cut for us and made not-sharp from a larger pirceof metal 'dowel'. The sleevie-thingies can be bought online from most tent places (eg. Panther), and since we still have to get one I'll let you know where we find ours!

As far as canvas tarps, what about painter's drop cloths?