You cant drop these special costumes ingame.
IMPORTANT:
You can exchange your Alz or your playtime to Webshop points.
Alz to WS points:
-hit the 6th button on the left side on their homepage
-login and exchange your Alz (you need to be offline ingame)
-1 b Alz = 100 points
Playtime to WS points:
-click the 7th button and login
-press the left button then (1 hour onlinetime = 30 points)
WORKS ONLY WITH Internet Explorer!
EDIT: the 8th button is for the Webshop