Check this guy out - 330mate.com. He sells a ton of stones out of Japan for the purpose of sharpening chisels and planes, knives and swords. I recently bought 2 damascus chefs knives from him off of ebay. They were shipped in decent time, in good condition and as described. His communication is a bit poor, but his products are good.

Here is a link to his ebay store:

Shop eBay Canada Store - Japanese tools whetstone for sword:: Hi class, Yamawaku

Here is a link to his website:

天然ç¥çŸ³ æ„›åª›ã€€ä¼Šè±«éŠ˜ç¥ ã‚ãŒå›½åˆã®å¤©ç„¶ç¥çŸ³

Now, his website is quite difficult to understand becasue it in Japanese for the most part. But, what I did was use Google Translate to figure things out on his site.
Google Translate

Anyway, I thought I would share. I hope this can help you out.