iRiver's Hong Kong site has the iMP-900 remote -- which is identical to the H300 remote! I bought one from them for HK$320, or about US$41. (I picked it up in person while visiting HK.) A ridiculous luxury for me this late in my H320's life, but I love the look of the thing. What's even more ridiculous is that last year I bought TWO of the Slim 550 remotes here in Beijing!
Anyway, here's the site, navigate to Accessories by clicking on the headphone icon:
http://shop.iriverhk.com/
It was on the third page of accessories a minute ago.
They also had H300 cradles, the external battery pack, and the two-piece leather cases (a bit nicer than the stock windowed cases supplied in the U.S., but I would just go for a latex skin instead). To find them, though, you might need to navigate using the text links at the bottom of the page.
Unfortunately, their HK website is all in Chinese, but if you contact them I'm sure they should be able to help you in English. I never asked them if they shipped internationally, though.