I haven't seen any shops with a decent selection, i.e., with larger sizes and also the western shell (Asian shells are rounder, I think). When I asked shops if they'd be willing to put a 2xl or 3xl on the shelf, they all refused (including the below two shops), saying they'd only order one if I paid for it in advance -- even though I'd have no guarantee that it would fit!
That's why I ordered all my Arais from abroad.
If you have a small or medium head, just try the shop at Bade & Jilong, or the one at the north end of Ruiguang St. in Neihu (see directions below), and try on the Arais that they have. For a long oval head, try on the Arai Signet. You're also quite welcome to stop by my apartment to try on our Arais (L, XL, 2XL, 3XL), KBC, Roof Boxer, Caberg, Vegas, Bell, and so on -- if you find one that fits you can then order one by mail order without worrying that it won't fit. I also have a few nice helmets (not Arai) for sale at a discount (ones that didn't fit us). Just drop me a PM.
Directions to Ruiguang shop:
(Berlin DYnamic Industry Co. Motorcycles and Accessories: 1F, #588, Ruiguang Rd., Neihu)
Heading east on Minquan, go past the bridge, Costco, under a freeway, to a gas station on the right and China Times bldg. on left. At that intersection, Ruiguang St., turn left (north) and go 19/20ths of the way to the end of the road (a few km.). On the left will be a 2-story plate-glass storefront with big bikes or gear visible, often with a big bike or two parked out front.
The manager is Lewis Li (he goes by Xiao3 Li3 in Chinese). Very friendy, helpful guy. The phone # is 2799-5430.
See also these threads:
http://www.forumosa.com/taiwan/viewtopi ... 10&start=0
http://www.forumosa.com/taiwan/viewtopi ... 68&start=0