Why do you need to buy new ones? Are the original ones missing, or broken. Otherwise, couldn't you re-use your existing rails. I assume you have the original wood rails, but they're leaking like mine, or broken.
If your rails are broken, you could buy two teak pieces of wood and use the old rails as a pattern to cut the new ones. Use a band saw for the rough cut, and a sander to finish off the edges.
Drill holes in the rails to match deck holes, and caulk with polysulfide (Do NOT use silicon - silicone is useless on a boat except maybe as a temporary fix at port lights).
