Get the national dex (see all 210 pokemon) and the people blocking the way to stark mount move. There will be the guy with ginger hair with you (can't remember his name) and team galactic with it's new boss will be there. The police guy comes and you go back to the fight area and you can go into the gym leaders club (where you can battle them again!). Go back to stark mountain and heatran will be there. It is lv 50 and can be a male or female, just keep turning it off and on again until you have the gender you want. Also you can battle your rival outside the club as many times as you want! Hope this helped.
You don't need heatran to get the national pokedex you are prolly missing rotom or manaphy rotom is in eterna forest in the mansion at 8pm in the tv and manaphy is in the book at the rich guys house
Use an action replay and go walking
I have to find heatran to get the national pokedex but how do I do that if stark mountain is blocked?
Get national dex and go up