I recently spent a couple of years working at real, old-fashioned, locally-owned lumber yard. The kept heavy, nasty, rough 2" x 12" x 20' red oak in stock. The only people that bought it were folks looking to re-deck lowboys. They also sold screws called "tech reamers w/ wings." They are a counter sunk self-drilling screw that has wings that cut the countersink hole and then break off while the self-drilling tip drills through the wood and then into the metal cross members. We sold a fair amount of those screws and didn't hear any complaints. I guess the moral of this story is to find a real lumber yard, if you can. They can find almost anything--for a price--and have sources for milling the lumber, etc. The guys I worked for even located some tongue and groove apitong for a government project.