Avoid the website mentioned in answer number 2 above. I make presentations at rendezvous all over the Midwest and at my seminar I demonstrates Napier's Bones. I, unfortunately, bought a set from an eBay dealer who sells the very same set,
http://www.uniquecanes.com. The construction was terrible. The rods were not even square. The tabulat's index rod was not square to the tabulat, and the silk-screen printing did not align correctly, especially for the square root and cube root rods. The box the set came in, however, was well constructed. I had a great deal of difficulty trying to convince "ajsfixit" to make amends. He never did. the price of the set was approx `$80`

,but I think it is now available for around `$45`

. Finally, the set is not a replication of Napier's Rods, if you're interested in historical accuracy. My recommendation: depending on how authentic you desire, study up on the rods via Google and then have a local craftsman make a set for you.