Is there a wall mount retro fit for iMac deskto

The 27 in can I'm not sure about the 21.5 but I don;t think so.

SeeiMac (21.5 and 27-inch, Mid 2010) - Technical Specifications if that is your model.

Message was edited by: Frank Caggiano - Of course that is for a true vesa mount. There might be other 3rd party solutions for a 21.5 in iMac.

If your iMac is one of these models, there is an adaptor kit available from the online Apple Store:

VESA Mount Adapter Kit for iMac

Here is the video showing how its installed:

fitting the VESA Kit

As Frank suggests, there is another solution for wall and arm mounting that does not require removing the stand.

see > iMac Mount, iMac VESA Mount Adapter Kit for 27, 24, 21.5, 20 iMac