There are quite many good alternatives to Google and having them in your tool belt will help you to find lots of interesting sources.
Some ideas where to look – some of these are methods that I use myself quite frequently:
• Reddit’s search function – even more useful if you know a good subreddit relevant to the topic at hand. Subreddits are easy to find if you google for ⟬topic subreddit⟭
• Google Books. Lots of high-quality material there.
• Archives of digitized newspapers. Lots of high-quality material there as well. Which archive to use depends on your language and locale. Here’s one example: https://news.ycombinator.com/item?id=28140621
• Internet Archive. Their collections include many good scanned books, technical manuals, etc. ⟬site:archive.org *keyword⟭ works well.
• Twitter’s search function can sometimes yield links to good articles, blog posts etc. It depends on the topic, but there are lots of nerds on Twitter discussing the topics close to their hearts.
• Old–school web forums. Those still exists and many of them are searchable. (Can’t think of any specific forums that are in English, but there ought to be some good ones still out there.)
• “Trade rags” (i.e. a newspaper or other publication that covers a particular industry). Many of those are not paywalled. Can possibly be found by using the methods listed above.
Best of luck!