HTML
https://html5up.net/
https://buildfaster.co/
https://colorlib.com/wp/templates/
& Bootstrap
http://organicthemes.com/themes/
https://www.creative-tim.com/
http://bootswatch.com/
WordPress
http://organicthemes.com/themes/
dessign.net/premium-themes/
& Bootstrap
https://wptavern.com/18-free-wordpress-themes-built-with-bootstrap