Before I post the new stencil, let me just show you how it came to be (I needed to do something, which required me to do something else, which in turn caused me to need to create this):
Anyway, here’s the stencil. It’s version .1 so don’t make fun: AWS.gstencil.
To install the stencil, download, extract from the zip and then open. When prompted, click on Move to move it to the Stencils directory.
Reopen OmniGraffle and create a new object. Under the list of stencils, select AWS and you’ll see the objects on the right to drag into your doc.
Good luck writing/documenting/flowcharting!