Mike lists the main stores but there are a few others (
http://www.relec.ch) Quarks Amigalounge (
http://amigalounge.com/),
http://www.commodorecomputercenter.com, icomp.de (Jen's Individual Computers), and of course Elbox.com.
If you have a specific request, some of the horrible, evil, ugly-to-the-core hoarders out there (because they won't sell their stuff for a fraction of what they paid for it) might have boxed something in a water proof, sealed plastic bin kept indoors in room temperature & humidity for prosperity sake, and might be convinced to sell it to someone who does not troll the forums looking for a fight. To reach these scums of the earth (not the trolls, they will FIND YOU), you can use clairvoyance or telepathy, but an ad in the Marketplace here or in the Wanted section of Amibay (as Mike suggested) may work better.