Go to www.Amazon.co.jp
Scroll all the way to the bottom of the page and look for the globe icon.
Change the language to English (assuming that’s what you read)
Move back to the top and you can sign up with a very similar process to the US version of Amazon.
Put in your search term. Try to keep the terms very basic or use part numbers whenever possible. Chassis codes are also a great idea. Unfortunately there is a lot lost in the translation which make it take a bit longer to find what you are looking for sometimes. This is also why I’ve started making the parts lists here.
This is less a requirement than a suggestion, but in the search options on the left bank is an option for “International Shipping Eligible”. Click this and save yourself a lot of heartache. Many items are over sized for DHL, and would require you to use a shipping relay service. I have not tried any of those yet, and have no suggestions for you on which one to try if you do.