Hi:
I have the 28 inch Apollo version.
Is this what you are looking for?
Apollo Mono Mounting Arm | Westcott Pro Photography and Video Lighting
Here is the Adorama link--where I bought mine:
apollo mounting arm
The Adorama link indicates it is for the 28, but the Westcott link seems to say it is for both.
I like the Apollo 28, but the mounting arm actually is a bit of a pain to use. I find I just deal with the limitations that exists without the mounting arm. It is inexpensive, though, so it may be worth a try. It comes with no instructions.
Here is a DIY link:
28" Westcott Apollo with DIY Mounting Arm on Flickr - Photo Sharing!
There is another link somewhere on my computer that shows how to use the Westcott mounting arm with some useful photos--I will look for it.
Hope the above helps.
Gregg