you could attempt to contact gamma. i've had mixed results with them. mostly it's hard to get a hold of them period. they are generally helpful once you get them though.
the bracket itself should be easy to make. it is basically a flat plat plate. if you are handy with fabbing should be a doable or any shop would be able to make one for you.
edit: i uploaded the manual to my dropbox. you can see the bracket on page 78.
Stage 1.5 Installation Manual