I recently discovered paper and envelopes for correspondence that I like, made by a Japanese firm, Okina. I was in a brick and mortar shop where a tablet caught my eye. It had a retro '60s "Air Mail" cover. The paper is a traditional lightweight almost onionskin for airmail, and has faint lines imprinted just to the margins (see below). It is B5 size at 18 x 25cm. Okina airmail envelopes to accommodate the B5 paper are also available. Fountain pen inks that I've used so far have not bled through or feathered.
The largely Japanese-language company website is: http://www.okina.co.jp I was unable to find the same tablet with the retro cover, but what appears to be the same paper with a different cover is Eternal or Princess. The matching envelopes are Air Mail.
Okina also offers a wide selection of correspondence paper and envelopes designed for writing Japanese in vertical fashion. If you cannot read Japanese, the only way to find what you want is to browse the website's warren of links. If there are any Japanese readers among you, please share anything of note from the Okina website, including the name of the distributor or retailers in North America.
