Even if you don’t have any “Hero Hunting” items you can still get new heroes. Every few hours new heroes will show up in your inn. I heard someone say every hour and someone else say it takes 3-4 hours. Even if you don’t have a “hero hunting” item you can simply wait for new heroes to arrive in your inn. Check back with you inn and you’ll see new heroes.
If you are going to apply a “Hero Hunting” item to find new heroes in your Inn, do not waste it on a small Inn with only 1 or 2 heroes. The higher the level of your inn the more heroes that will be available.
A level 2 inn will have 2 heroes. A level 4 inn will have 4 heroes.
When you apply hero hunting all the heroes in the inn will be replaced with new heroes. If you do a hero hunting with a level 4 inn you have twice as many chances to find a good hero as an inn that is level 2. (You’ll get 4 new heroes to pick from instead of 2.) If you use a hero hunting with a level 8 inn you have even more chances. You have an opportunity to get 8 new heroes at once.