Do you know what size (OD) you need? Can you measure the OD of the threads? Number 6 is pretty large. I have some #2 and #4 which we had in stock but not on the cart. I'll get them up later today if interested. However, it may not be worth it if just ordering the screws. We do have a flat $6.99 shipping fee no matter what you order but again...if just ordering the screws you'll likely pay more for shipping no matter where you get it from. Finding it locally would be the best ... if not too far away.
Check out this chart:
http://www.engineersedge.com/screw_threads_chart.htm