Well folks, its finally happened. Yes, Noah are in a happy enough state to start offering mail order merchandise again. Not since the dark days of November 2016 when the shop shut and merch was only sold at venues has this been a possibility. "Noah The Shop" can be found here.
The downside, they don't (and never have) deliver internationally.
The upside for Noah fans based outside of Japan? There is a way via two companies who specialize in shipping goods from Japan for you.
Items are going quickly, and more will be added. At the time of writing (May 2018) you will get a free Noah sticker with your purchase. Limited edition items may not be added, as all goods are what are sold at venues (so you probably won't find the replica of Marufuji's necklace).
White Rabbit Express
This is the quickest and easiest way (if not the cheapest) to buy from Japan. The website is in English, and it takes you step by step through what you need to do.
However I would recommend putting in the item name in Japanese to be more precise about what you want (as much as he probably hates the idea, not everyone knows who Kenoh is).
Tenso is the second shipping site that has been recommended to me (I have set the link to go automatically to the English part of the site). You will need to create an account and then go through the steps. It will give you a special Japanese shipping address that you can use on all and any Japanese sites to buy products.
If you wish to register, please do not be put off by the part which tells you to "Enter your name in Alphabet" - this is in case you come from a country with Cyrillic or Arabic script etc.
HOWEVER after registration it will ask you to submit proof of identity documentation, this is due to Japanese law. If you don't wish to do this, you can sign up with Buyee, I don't know if it will be compatible with the Noah site though; but it is compatible with Amazon.co.jp.
A few months ago, Amazon did stock Noah products (i.e. the 2018 calendar, the acrylic keyrings and card holders), however the last time I looked Noah didn't seem to have a storefront there anymore. If there is an item you do want I suggest you look for it on either Amazon.co.uk or Amazon US to see if they stock it. They don't stock everything, but I have managed to source most of my book and CD Noah library from outside of Japan.