Following on S. Okada's post, I recently ordered 12 boxes (864 pieces) for just under $25 per box, or 3 sticks/dollar. Rakuten only ships within Japan, but Tenso
will forward the package abroad for roughly twice the cost of the package itself. However, Tenso is having a promotion till 28 Feb 2012, first 5000 yen discounted to 1000 yen. For a few boxes, jump on this, this is your chance. I went way over so it didn't save me much.
Even though Rakuten won't ship the chalk abroad, their English web form requires a complete US address before a person gets to look at the order. This is easy: Give your US address, but in the comments field, give your Tenso address. This worked just fine for me.
My credit card company put a fraud alert on Rakuten's charge, which canceled the order. Somewhat reasonable if Rakuten doesn't ship to the US, where I am. I had to place the order again, after clearing the fraud alert. Better to warn your credit card company in advance.
My breakdown, 12 boxes was 7092 yen plus 300 yen shipping to Tenso, or 92.62 USD. It arrived within a day. Tenso to NY was 17300 yen shipping plus 2980 yen handling, minus my 4000 yen coupon, or 204.41 USD. If anyone can parse a "slow boat" shipping option that costs less, that would help. Otherwise, I have word of a new importer to the US that should have stock in May, also $25 per box but less adventure to order. I'll post again when that's official.