I've seen some segmented mandrells (imagine tiers of cakes instead of a taper) online as well. I'd Check Amazon or Fire Mountian Gems and Beads, both may have them.

EDIT: Something like this? https://www.amazon.com/dp/B00V9K4X8U/ref=cm_sw_r_cp_apa_3pOBBbBTRKEBG