Here in the US, I see Thunderbolt peripherals available at a number of online and storefront locations.
Apple Store
Fry's
Micro Center
B&H Photo and Video
Amazon
Newegg
eBay
and at many Mac centric stores
Seagate, LaCie, WD, and G-Tech seem to be the most prominent and widely available. El Gato, Caldigit, and Monster less so. And there are many others
On the Windows side, I've seen computers from Dell, HP, Asus, Lenovo, and Acer.
For motherboards, there are Asus, Gigabyte, and MSI to name a few.
Google and other search engines are your friend in your quest.
Granted, you won't find "in your face" ads with blazing messages about Thunderbolt sales. You will need to read the reviews on internet retailers and internet publucations.
There us a website, www.thunderbolttechnology.net that also summarizes many products.
Perhaps what you are really asking is where are the best deals!