Here's a direct link to Nokia's theme download page:
Highly popular for the 3110c, often featuring digital clocks overlaid on floral backgrounds. Business Minimalist: nokia 3110c clock themes 1 link
Before clicking any link, scan the .nth files with VirusTotal. While rare, some malicious files were disguised as themes back in the day. Here's a direct link to Nokia's theme download
: Their catalog is regularly updated and allows you to view screenshots of the themes before downloading to see how the clock interface looks on the device. nokia 3110c clock themes 1 link
Tools for Windows (offline):