Is the problem finding beads with holes that are large enough? Often beads made of bone, horn, wood, or ceramic have larger holes. Lots of African beads have relatively large holes, too. I know that some hemp artisans also use a lot of polymer clay cane beads and pendants.
For an example of the beads I used recently in a men's beaded necklace, see this project:http://www.bellaonline.com/articles/art34301.asp
All of the beads I used there have holes that should be large enough for use with most hemp.
The most difficult beads to find with large holes will probably be gemstone beads (especially because the holes are larger on the ends and smaller on the insides) and some glass beads.
I recently reviewed a book called The Bead Directory which might help you guys figure out which beads would work best:http://www.bellaonline.com/articles/art33275.asp
Best of luck!