As someone once said getting gun owners organized to protect their own rights is like herding cats. For that reason I seriously doubt that they will get 1000 people to actually show up. For most people the problems will be either taking time off of work or affording the trip, and a poor showing will be taken as a sign of weakness. But even if a miracle happened and 1M people showed up - it would never make the news. The press would go into overdrive suppressing news of the event or at the vary least locating the 5 dumbest, most inarticulate, and heavily camouflaged attendees to interview and portray as average gun owners. SOP.
The place to start is state capitals. I know that even at 500 miles away I can find the time and funds to attend a state rally.