Every time I need to create a menu or toolbar with actions I end up collecting some images extracted from different application and hand tuning them with the image editor. This
You can search on Web. There are many sites with icons; I use these:
Surely there are more.
You can search icons by name or cathegory, search similar icons, icons by packages,...
Regards.
@PA check this link.
my favorite famfamfam
and these questions in SO
and so on.