Google, Bing and DuckDuckGo will usually get the same results. I mainly use Google because you can specify a time or size but that isn't always helpful. Team websites which includes their facebook, twitter, instagram, etc sites. Newspaper sites near the team are good. SportsLogos.net is also good. This site is good for concepts.
https://www.sportslogos.net/index.php
Wordmarks can be hard to find. Sometimes I have to use T-Shirt/clothing sites. Sometimes you have to trace the image yourself to make a useable image. Fathead, Fanatics, team's websites, college websites, ebay, amazon. Basically anywhere.
https://fathead.com/
https://www.fanatics.com/