Fiery Field... I think there are 30, but I haven't played the game in ages, so I could be wrong.
For Zapdos and Moltres, first make sure you have enough room on your team, meaning you should have no more than two size-1 Pok�mon with you. Their recruitment rate is 30, so you probably won't get them on the first try, but they're not hard to defeat, so just keep trying if you don't get them at first. But it's guaranteed they won't join if there's not enough room on your team while heading up.