I don't know for sure, but I would try the following places first:

Art's Hobbies - he has various CF materials & components: http://www.arts-hobby.com/store/

Aerospace Composites: http://www.acp-composites.com/acp-cr.htm

I know that BV also has some carbon rods, but I don't know what kind of selection he has (the locating dowels on my Super Bandit stab are either 6mm or 1/4" dowel)

Hope that may help.

Gordon