Moina is notoriously difficult to find.
But as John asks for a European address, I can tell him two addresses from Germany:
1) http://www.moinashop.de and
2) http://www.interaquaristik.de
Both are prepared to ship Moina within Germany. I don’t know whether they do this across the country’s borders, but you can try and ask.
At 1) it’s easy to find, since the whole shop is called “moinashop”; it only sells very few things, among them Moina macrocopa, the “Japanischer Wasserfloh”.
At 2) it’s more difficult. Look for “Futter”, then go to “Lebendfutter” (live food) and then look for Moina macrocopa, “Japanischer Wasserfloh”.
And ask them whether they will ship these to … Good luck.
(By the way: Mostly one single small stock is too small. Take at least three of them).