BuddyPress.org

Couldn’t you create your own loop that calls the groups forums that you want. Then repeat it a few times for each group forum you want to list?

if ( bp_has_groups( ‘slug=GroupName’) ) :
locate_template( array( ‘forums/forums-loop.php’ ), true )
endif;

Or what about the forum extra’s plugin? https://wordpress.org/extend/plugins/buddypress-group-forum-extras/