Thanks All for the replies!
Is there an acrylic fabricator here on PT? I asked about this on RC, but got no bites. I have some tools at home (built my ADA stand) and could do it myself, but to be quite honest-I have a lot going on with work and grad school and don't have the time to make myself smart on acrylic joinery, etc.
The brackets I want to build would be thicker than the 10mm glass of my 90-H. The fixture that these brackets support is a 36" buildmyLED fixture. With this thickness and the light weight of the fixture I can't see warping being much of an issue.
I have attached a screen shot of the bracket in mind.