If anybody is still looking for an air assist nozzle for their laser I can confirm that this one:
http://www.lightobject.com/1820mm-Laser-head-w-air-assisted-Ideal-for-K40-machine-P701.aspxdrops right in. It replaces the mirror and lens holder from this one:
http://www.lightobject.com/1820mm-Focus-lens-Mount-P204.aspxThe one I received didn't have the elaborate right angle air fitting, just a straight barbed one.
I think that is actually better for my setup.
The way it fits together is much nicer than the silver one. It actually holds the lens centered when you assemble it.
To get the mounting plate you will have to make it, or buy the silver one, but it makes adding air assist very easy.