Tenso is probably the most famous proxy shipping for now:
http://www.tenso.com/
And they have an associate site that is for proxy purchasing called Buyee:
http://buyee.jp/
Both sites have display language options. I've been using Goyokikiya myself recently though. They also have proxy shipping and proxy purchasing, but don't have english interface:
https://www.goyokikiya.com/
In general, Tenso is more convient that you don't have to register what you buy, Buyee have the advantage of discount for buying from certain sites, and Goyokikiya is cheaper when you have multiple packages receiving from different shops within 1 month, that they don't charge you extra with repacking multiple packages for less weight. Check their pricing scheme and
service charges for detailed costs.
In your case, since Kadokawa shop doesn't accept overseas credit cards, you either find another shop that accept overseas card or use proxy purchase service. But I suspect you won't find cheaper shop than Kadokawa shop for that one.
I heard if you have JCB cards it can treated as local cards, but I haven't tried it myself.