The recommended implementation is an Hgroup of ToggleButtons.
A button bar is a logical grouping of buttons, and helps to differentiate between sets of grouped buttons. A HGroup of buttons may not always cut it. e.g: in most text editors, the bold/italic/underline functions are implemented this way and it has to be a buttonbar to differentiate between the next set of buttons (i.e: bullets/numbered bullets).
That being said, this is different from the spark buttonbar, as a navigator it has to select only a single item. I think the type of buttonbar you're after would be used as an alternative to a checkbox list in a limited space UI.
I've been searching for the same and found an extension to the mx:ToggleButtonBar which may work for you: