The store that we get our Zaurii from is a place called Nani wa Denki - it's consistently one of the cheapest places to find them. I just had a friend pick up my brand new 3100 for 530,000Y (about $513 CAN). The branch we go to is in Osaka, though. Not sure if there's one in the Tokyo region.
The pentopia stylus is nice. I wanted my friend to pick another up for me, but he couldn't find one
The 3100 comes with a world power adapter, so you don't have to worry about it. I've never had a problem using the 100v adapters here in Canada, and I've had 5 or 6 of them.
As for the host cables, I've finally found them for sale here in Canada - Both the goldx and some no-name. They were both at the "Source", AKA Circuit City - what used to be our Radio Shacks.