I think any bead can work.
You can make a rosary with any beads you have, some traditions use a cord (string) with knots along the length. The purpose of the bead or knot is a tactile reminder of a specific prayer- so by extension then the rosary of the very humble and the truely wicked would be very long!
A Christian store seems like the first place to look for a rosary. A quick Internet search shows a nice-looking one from RosaryMarket.com for $10.49 after shipping. http://www.google.com/products?q=rosary&scoring=p&cat=188 Of course, you could use Instructables: http://www.instructables.com/id/How-to-make-a-Rosary/