Try putting your topic in the search box for Gale Ebooks. Look at the titles of the encyclopedias that are found in order to find the most relevant search results.
Try searching your topic here. For Encyclopedia Britannica, you might need to pick an article that is more general than your search term. For example, when I searched "coffee trade", the article about Latin America had the best information about growing and selling coffee for money. You can use Ctrl + F to search for your topic in an article.