How do I find people to email advertise to?

[Kim Cunnings]

Your efforts will be much more effective, if you build your own list of subscribers who knowingly and willingly provide their email address to you. Or phone number, don't know if you are considering SMS advertising.

For example, this store in my area told me they'd notify me by phone/email next time they have a sale. I did give them my phone number, they did notify me = everyone was happy in the end.
You can instruct your employees to prompt people to leave their email for whatever reason.
But then, if you tell them you will write to them when you have new items in stock (just an example), you shouldn't be really writing to them about anything else.
Usually email marketers use separate lists of contacts. For example, you have a list of people who singed up for the news, or the coupons, etc.

Another way to build an email base is to have a promo campaign of some kind (unleash your marketing genius to come up with one) and ask people to leave their emails if they want to enter.

When they sign up you ask them if they want to receive updates from you. If they say YES, you sign them up. Or you could have a checkbox already checked by default.
Alternatively, you could have a pop-up form on your site or landing page that prompts people to sing up for whatever you want to send them.

But think about it upfront. let's say, if I subscribed today, it'd be most effective to send me a follow-up email the same day, and then another one within a certain period of time.
If you don't write to them on a regular basis, they may forget all about you. The ideal way to do it is to establish a certain periodicity. Research shows people are least of all irritated by emails they expect to receive.