30Hz Refresh Rate, how to tell if supported?

I would like to buy a new monitor or TV for Prepar3D.  Now it just so happens on my set up the best experience is to run frame rate unlimited on the simulator, so long as the display is the providing the limit via a 30Hz refresh rate.  My BenQ monitor only support 60Hz so that's no good, and I have one old Samsung LED TV that can do 30Hz and another that cannot (it can do 30Hz interlaced, but in the simulator that is 60 fps).

Most TV and monitor specifications will give you a headline rate of say 60Hz or 120Hz, whatever makes it look good on the sales page.  The question then is, how can I be sure I'm getting a device that can support a "real" 30Hz (i.e. 30hz progressive scan on a TV)?

Thanks

Simon