[chrishajer]

https://plugins-dev.bbpress.org/browser/bbpress-sitemap-generator/trunk/bbpress_sitemap.php?rev=1277

https://bbpress.org/plugins/topic/bbpress-sitemap-generator/

http://boakes.org/talk/topic/sitemap-plugin-for-bbpress

The first link is probably best since development of the plugin has been picked up by someone else.