Michaels sells sets of small and large ball end embossing styluses for $5 a set:
Mandala
Dotting Tools with Colorful Handles by Craft Smart: ø1, 1.5, 2.5, 3mm
Mandala
Dotting Tools by Craft Smart: ø4, 6, 8, 11, 12, 18.5mm
They also come with "dotting dowels" of several diameters, which are handy as tube rolling mandrels.
Alternatively, these are $6-7 a set:
Wendy Vecchi Make Art
Perfect Stylus Set: ø1, 1.5, 2.5, 3mm
Wendy Vecchi Make Art
Perfect Stylus Set 2: ø4, 6, 8, 10mm
(Other folks have mentioned these before; I just wanted to put them in an easy-to-find place for people who might not have run across them.)
Does anyone know of a set of cone rolling mandrels of various angles? My pencil sharpener only does one angle of course, and found objects aren't really getting the job done, so it would be nice to have purpose-made cone mandrels.