The Agilent DSO/MSO6000 series of scopes (and presumably the 5000 and 7000 models) provides the same triggering for its FFT display as it does for the rest of the waveform acquisition process, so that might be one option.
They can actually do a lot of things that the Tek MDO marketing literature might lead you to believe are brand-new features that have never been available in any form. That's probably true of many scope models, but I'm only familiar with triggered FFTs on mine.