I've seen preorders for seekers expansion for 360 on newegg.com recently. Don't know if they are still taking preorders now though.
EDIT: looks like they are: http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&N=-1&isNodeId=1&Description=seekers+of+adoulin&x=0&y=0
Edited, Feb 26th 2013 3:30pm by mokatu