In the video preview window, the last two icons on the right produce snapshots of what is visible in the preview window. The disc icon will save the image to disc the other icon will place snapshot on clipboard for copy to another program. Someone corrected me if this is wrong, but I think you should set preview mode to best full to get the highest quality still.
Before scrolling to find the exact frame you want, maybe you could try un-checking the "smart resample" box and check the "no resampling" box by right-clicking the event in the timeline, then choosing Switches. I'm not sure but maybe it will somehow facilitate your search by getting rid of "created frames" between the actual real frames you shot...
Just a thought but maybe it'll be worth it (maybe not but what the heck, it takes five seconds to do it)...