once you fitted the vesa mount adapter you just need a ordinary wall mount for a TV (these scaffolding type things for example ), but they all offer the holes for vesa mounting , you only have to watch the weight limits carefully as some are only designed for 19 inch lcd tv's which weight half of a iMac , others are designed to hold a 100" plasma tv , so just type in google vesa wall mount and you find lots of them
but not to close to the wall ,you NEED circulation of air between wall and iMac if you got a aluminium iMac