How do you get more heroes?

A bunch of ways.

1. Buy them with $$$

2. Use your different coins you either get free each day or find at Noah's Tavern.

3. Join Rallies with allies in alliance to earn chests that oftentimes have "Choose your card" type items that allow you to choose from a limited variety of heroes.

4. Event prizes, event prizes, and event prizes!

5. At Lvl 12 stronghold you can go to the ruins and buy cards for certain heroes there.

6. Finally, the most obvious and the one you will only do when you have stamina and no one to rally with, you can just kill the solo zombies on map.

There are other ways like cashing back old excess cards to choose others, using points in arena to buy...but theres no end to the number of ways. Some are just faster than others