eMarketer contains some performance metrics (e.g. CPM, CPC and CTR) for seven channels—Display, Email, Mobile, Retail & Ecommerce, Search, Social Media and Video. Search for these titles, then explore the database further using your own search terms.
Note: when viewing the performance metrics you can use the drop-down box to change geography to US, Worldwide, or another country. Data availability is different depending on the geographic area selected.
10-K Annual Filing (for public companies)
It's possible that you will find some information about advertising expenditures in the company's annual 10-K filing. See the Company Research Guide for more information about locating 10-K filings.
Search for news articles and press releases that may mention advertising expenditures for a company, brand or product. Recommended databases: