There are several ways to find websites that have Google AdSense activated for a specific niche:

1. Google Search: Perform a Google search for keywords related to your niche and look for websites that display Google AdSense ads. You can use search operators such as "site:example.com" to search within specific domains.

2. AdSense Directory: Google used to have an AdSense Publisher directory that allowed you to search for websites in specific categories. However, this directory is no longer available as of February 2021.

3. Niche Forums and Communities: Look for forums, communities, or social media groups related to your niche. Often, website owners in a particular niche will discuss their AdSense earnings or display AdSense ads on their websites. Engaging with these communities can help you find relevant websites.

4. Competitor Analysis: Look at your competitors' websites and check if they have AdSense ads displayed. Tools like SimilarWeb or SEMrush can provide insights on the top advertisers for a specific website, including AdSense.

5. AdSense Publishers: While it's not possible to directly search for AdSense-enabled websites by niche, you can check specific AdSense publishers to see the websites they own. AdSense publishers can be discovered by checking websites that display AdSense ads and identifying their publisher IDs.

Remember, it's important to respect the privacy and terms of service of website owners when searching for websites with AdSense ads.