Raw, preferibly still in its casing. We used to be able to get in Hualian. Has anyone seen it in Wulai or any other local Aboigine/South East Asian population centers?
Are you looking for live plants, or prepared material for use? I have seen some places in that huge nursery area in Chaiyi (the one south of Taijong, i think i spelled it right?)selling plants.
I am planning to make it into vigoron, so I would need the root. OTOH, if you plant them, we’ll buy 'em. 
Are you thinking of yuca (with one c), a root vegetable also known as cassava (Manihot esculenta), by any chance?
Correction made.
I want this:
To be turned into this:
In Chinese it’s called 木薯 (mu4 shu3). But when I Google for 木薯 and 台灣 (Taiwan), all I get is articles about some farmer who poisoned himself by eating home-grown cassava roots. (They have to be cooked very well to get all the natural cyanide out.)
Yep, those and the pejibaye, though tasty, have to be throughly cooked. Nothing some mayo won’t fix. Taiwanese aboriginals are quite fond of it, and there are lots of products that use yuca flour, so it is big in production. But, alas, it is hard to find in its elementary form.