Actually they're called Tetra. Variable is for a weapon.

Tidus - Variable Steel, Tetra Shield
Yuna - Malleable Staff, Tetra Ring
Lulu - Morhping Mog, Tetra Bangle
Wakka - All-Rounder, Tetra Amrguard
Kimahri - Shapeshifter, Tetra Armlet
Auron - Shiranui, Tetra Bracer
Rikku - Flexible Arm, Tetra Targe

Wantz in southern Macalania Woods sells these things for 100,000 gil each, after you've (SPOILER)seen the Highbridge scenes when you have the airship permanently, and as long as you talked to him on Gagazet.

Edit: Ribbon does not, to my knowledge, exist in the NTSC-US version of the game, only PAL and NTSC-J (International).