You can buy from Muscara. He is very reliable and reasonably priced, the website has pretty much all the new Italian merchandise available.
My two favourite places are eBay and Yahoo Japan Auctions. I have a guide here on how to use YJA. If you have Livejournal, you can join SMCollector. It is a Sailor Moon selling/buying community but the application process is tough (to keep out scammers).