I have about 150 items of Japan and Korea (South) up for sale on eBay right now.
Everything is fixed price, buy-it-now, so if you like it, you can get it right then!
All items have free shipping within the US.
(International shipping is between $3.50-4.50 and flat-rate, meaning that whatever the highest single-item rate is, that's all you pay, and all the other items ride for free.)
Please "add to cart" and check out at the end, rather than "buy now" and paying for one item at a time, in order to get the combined international shipping, and in order to help me keep offering free US shipping.
For Japan, there are a lot of harder-to-find items, including never-folded mnh prefectural booklet panes, some special recent booklets, a selection of full sheets, and a few longer commemorative sets.
For Korea, there are some nice mint sets, intact strips, etc, plus both mint and used souvenir sheets.
Also listed for both countries are some nice semi-postals and airmails (including Japan's only airmail coil, both single and pair).
I also have a couple of recent Japan issues, including the 2015 Philately Week (purty!) and a special half-sheet of Japan's issue of the "Gifts of Friendship" dogwood, that was a semi-joint issue with the US this past spring.
http://www.ebay.com/sch/the.philatarium/m.htmlor click on the little eBay button by my name.
Here are just a couple of pics for starters:
That half sheet, available only through the USPS (not available in Japan):

Philately Week this year:

Please don't hesitate to contact me through here or eBay with any questions you have.
And thanks for looking!