If you are looking for brand email contacts, a good place to start is by sending a DM on Instagram and asking for their marketing contact.
You can also use google to find PR and marketing contacts. Type BRAND+PR CONTACT in the search bar. You can look at any recent press release and usually the PR manager name will be at the bottom, or mentioned in the release or article.
LinkedIn is a great way to find contact information for brands. The company pages list employees and their roles, and often times LinkedIn gives you the option to message directly.