Just going to
www.eBay.fr will provide the widest variety, bar none.
If you want to buy without worrying about bidding, you can pick up the more basic stuff at
www.cdandlp.com, though that has fewer protections than eBay.
The site
www.musicstack.com also has a reasonable collection of merchants selling Alizée items. These are generally the most predictable of the lot - usually only CD's and vinyls, though occasionally something else.
For official En Concert merchandise, such as still exists in stock, you can get it at
www.charmandising.com. Be aware, however, that the shipping cost to the USA, if this is where you are, is huge. Unlike the previous three, however, this is an official merchant, not just a reseller portal.
The best assortment I've ever seen is on
www.priceminister.com. They, however, do not ship to the USA. It has broken my heart many times, and I no longer even look there, as it just makes me sad every time.
There is always something at
www.amazon.fr, but be careful there. Amazon isn't great about making sure the picture matches the item, especially when it comes to resellers using the marketplace.
Here's a picture of most of my current collection, primarily built from these sites:
